This is still a work in progress.

These are homebrew class features that strive not to make monk the BEST class or game breakingly OP, but rather, just give monks a definitive role to play in the game.

My thoughts on why monks aren't doing so well right now:

The main problem I see with monks currently is they're in the same space rangers were at the release of 5e. They didn't do anything really well outside of one or two incredibly niche features that had to be shoehorned into a campaign so that the ranger had something interesting to do, and the options they had otherwise were just weaker forms of things other classes did; they felt like playing a cleric that was always 2 spells away from being tapped out. They feel restricted, one-note, and honestly lacking for things to really DO besides bonk, and they don't even bonk as well as fighters.

Let monks be MONKS.

WOTC, stop trying to take the Asian out of the monk. Lean into it. People want to be monks because they like martial arts themed characters, and that includes the Asian culture that created them. I don't see anyone trying to take the crusader out of paladins, so let monks have the abilities that are as appropriate to them as scrolls are to wizards. Don't call ki discipline, stop flinching every time someone says weeb. Monks are the only class directly inspired by a non-western culture, so get over it or take them out of the game if you hate them that much.

A focus on identity

The aspects of the monk that are lacking mostly have nothing to do with their combat abilities. Yes, there are some aspects that need tweaking, but the rest of the monk kit are incredibly niche and don't read as 'monk' as much as they do 'I have no idea what to give them'. What the monk needs, especially at the higher levels, are not features that are low-level spells or immunity to magic they'll never be a victim of, but features that reinforce the identity of the monk as a class.
First and foremost, monks need to be the most mobile class in the game. If they have to sacrifice a decent AC for a frontline fighter, they need to have unparalleled ability to be exactly where they want, when they want. Unarmored movement is all well and good, but it's 2-dimensional thinking. We exist in 3 dimensions, so monks need to be as upwardly mobile as they are on a grid. When they jump, they should be as acrobatic as wire-fu action stars, flying over the heads of their enemies and springboarding off of walls and obstacles, not just running a little faster than most.

Sidebar, monks don't even run that fast. An average Olympic sprinter can cover 100 meters in 10 seconds. 100 meters is 328 feet. A real-life athlete can dash 196 feet in the 6 seconds of a turn, giving them a movement speed of 98. A level 15 monk in a world of dragons, magic, and ogres is slower, FAR slower, than a real-life human athlete. Way to make them feel supernaturally powerful.

Monks should be the one class that can, unassisted, cut a low-flying enemy out of the sky by skittering up a wall and leaping off of it to land a grapple by use of a wealth of mobility options given to them not just by their unique training, but also, by their need to restrict what they carry.

Weight, what?

Rather than putting a hard cap on being unable to wear ANY armor, monks should gain light armor proficiency and can claim the benefits of the standard unarmored movement/defense as long as the armor they wear is less than 15 lbs, which opens the door for them to be able to wear magically lightened armor, enabling them to stay in the pocket rather than having to scamper off behind cover after attacking.

Not just stuns

The core kit of monks shouldn't be limited to one condition effect. Yes, stunning is a powerful and a pain for DMs to deal with, but worse than that, it's tiresome for the player to only have access to one really strong ability, and all other rolls are just bonking. More than just being boring, it also doesn't feel very monkish.
Rather than nerfing the number of attempts a monk can make to stun to throw DMs a bone when their mighty encounter gets stunlocked by a few lucky rolls, monks should instead be focused on probing for weaknesses. More than any other martial class, monks should be the ones that expose the weaknesses of their enemies for the rest of the party to exploit. Shifting away from monks only having one option to disrupt an enemy will not only give monks more to do, but alleviate some of the frustration DMs have in dealing with endless stun attempts.
After all, if a monk has access to multiple types of debuff attacks tied to different ability scores, they'll probably use the one that's most likely to work, even if it's not as debilitating as a stun. While this might seem like simply trading endless stuns for some other endless debuff for the DM to deal with, the difference here would be that the monk player EARNED that endless debuff through investigation and experimentation. Any time a player actually puts thought into their actions in combat, that should be rewarded.

Expanded deflect missiles

The ability to deflect magic was a step in the right direction, but monks should be able to do even more with that ability, and it should unlock at a level before most casters are throwing spells that have so many damage dice that a monk would have almost no chance of reflecting it.

Hold your tongue

The tongue of the sun and moon ability at level 13 not only is useless due to how easily this can be mitigated by other classes at this point, but it doesn't make thematic sense for the class. This is more of a bard or warlock thing, not a monk thing, and they don't want it either. Instead, monks should get something that speaks to their identity more as a martial artist.

Timeless body? More like time to get an actual feature.

This is another 'I don't know what to put here' feature that doesn't benefit the kit nor character. At level 15, characters are clashing with demigods who can kill with a glance, why would they bother magically aging their victims? No longer need food? What, did you forget goodberry exists at virtually no cost by this point, even if you ARE keeping track of rations? This has also been replaced with a more thematic and sensible class feature.

New thematic homebrew class features:

Unburdened defense

Monks start with light armor proficiency, and wearing armor up to 10 lbs. allows them to add their WIS bonus to their AC on top of the usual DEX bonus. The average standard array monk with 17 DEX and 16 WIS would be able to wear leather for a respectable (But still lower than a well-armored fighter or cleric) 17 AC.

Unburdened movement

As long as monks are wearing armor no heavier than 10 lbs, they get the existing movement speed bonuses. At level 9, they may also run up vertical surfaces and may ignore difficult terrain penalties. 
In addition, when a monk jumps, rather than having to choose either to jump long OR high, they can do both at the same time.

If a monk forgoes armor entirely, they may use step of the wind at no ki cost as a bonus action once they unlock their ki abilities.

Universal homebrew rule: Aerial attacks

While in the air (At a height greater than you are tall), you may attack enemies even if you dashed on your turn while you're airborne. Because you're no longer occupied with running, you're free to attack an enemy that's in your path. So, if you're on horseback and leap off your steed or take a dashing leap out of a second story window, you still have access to your attack action if your target is in the path of your jump. However, if you dash, you must attack BEFORE you land or have a bonus action available.
Connecting with your target mid-air doesn't stop your momentum. You will continue on your path unless you choose to grapple your enemy in midair. If your attack misses, your opponent will have a chance to make a reaction attack against you.

Stunning strikes are now disabling strikes

At level 5, monks now have access to 4 different strikes to disable their enemies, and are no longer restricted to testing an enemy's CON.

Stunning strike: no change.
Silencing strike: Your opponent must make an INT save or be unable to speak until your next turn, as to land a hit to such a sensitive and easily protected area like the throat requires a degree of manipulation and deception to land successfully.
Staggering strike: Your opponent must make a DEX save or have their speed reduced to 0 until your next turn. If they roll a 1, they fall prone.
Withering strike: Your opponent must make a STR save or take a level of exhaustion until your next turn, up to level 3 exhaustion in the case of multiple withering strikes being landed in a turn.

Deflect missiles expanded

The added ability to deflect magic attacks in the new rules is a step in the right direction, but it comes in at level 13, when spells will be doing so much damage that a monk doesn't stand much of a chance to reflect it. It could stand to be expanded upon even further.
At level 6, monks may use their reaction if they're standing within 5 feet of an enemy targeted by an ally with a missed ranged attack to add 1D6+proficiency bonus to that ally's initial attack roll, potentially turning an ally's miss into a hit. This is basically the same thing as Tasha's Focused Aim ability, but applied to friendly missed attacks for added action economy benefit.
The ability to deflect spells is unlocked at level 10, when there's at least a chance of an enemy using a spell attack that's low-level enough to be deflected.

Step without shadow/dive attack

At level 9, monks may leap off of vertical surfaces or springboard off of objects to gain altitude. If they land on an enemy from a sufficient height, they may transfer the fall damage they would have received without slow fall to their target on top of their attack damage.

Shatterpoint touch replaces tongue of the sun and moon

At level 13, a monk can find the weak point in a structure to either break through and create a large opening or be silent and make just a small fissue big enough to see through. They may also use this ability to do extra damage to constructs and shatter shields.
To smash through a wall (meaning there's an open space on the other side), the monk rolls to attack as if they were a siege weapon and spends ki depending on what material it's made from. Wood/masonry: 1 point. Stone: 2 points. Reinforced/concrete: 3 points. The size of the opening is big enough for a medium sized creature to squeeze through.
To puncture a wall silently, the monk must pass a stealth check instead and spend the appropriate ki to create the crack, just big enough to see through.
Doing extra damage to constructs costs 2 ki points to deal double damage for a single attack.
Shattering a shield costs 1 ki point for a normal shield, and an additional 2 ki points to break a magic shield for every modifier point, so breaking a +3 shield would cost 7 ki points.

************** replaces timeless body

This is a work in progress.

Closing thoughts

Having monks be bar none the most mobile and least gear-dependent class gives them a clear identity in a party as a nimble scout and a weakness-probing melee fighter that needs few trinkets to do the things they do. Some of the changes are pretty strong, but frankly, monks need that, especially if the proposed changes in One D&D become hard baked.

Monks don't need to bonk harder, that's what fighters are for. Monks don't need to be half caster martials, that's what paladins and rangers are for. Monks need an identity that's all their own, and currently, there is no martial class built around massive mobility without resources and a much lower demand for being armed with multiple magical items.

These changes to the core features of the class would also make ALL the subclasses better. Shatterpoint touch could give Shadow monks the ability to infiltrate more easily by jumping into shadows they can see through a wall. The disabling strikes could expose an enemy's weakest ability scores to the rest of the group which could then be taken advantage of due to being able to probe 4 out of 6 ability scores instead of just CON, the most commonly high ability score found in opponents. Not only does this give relief to the DM in that the monk will have more options than just stunlocking a character, but it would also discourage metagaming, especially if your DM is in the habit of not using standard ability scores for monsters. If your players aren't sure what kind of abilities a monster has, then probing becomes all the more important, and the monk will have found their place in the team.

I've gotta give a hard NO to the idea of making the class even more restricted by forcing every single Monk player to meticulously monitor their carry weight. I get the idea for this concept thematically, but in function it just makes the class inherently less fun to play right out of the gate. I think one of the problems Monks have is that, because the class is required not to wear armor, Monk players need to boost both their DEX and their WIS... and because they're frontline fighters with just a D8 Hit Die, they basically also need to put points into CON as well. Rangers are in a similar situation, but a Ranger player can choose to prioritize spells that don't have a saving throw or attack roll, so while Rangers do rely on 3 Ability Scores, they still have room to experiment a bit.

With that in mind... I think just giving the class proficiency with Light Armor and just leaving Unarmored Defense as an optional feature would be fine. Similar to how Barbarians are capable of wearing Medium Armor, but they have the option to go fully armorless if they want to. I also think that a Monk's Ki save DC should get the option to use either their DEX or their WIS modifier... we already see stuff like Battlemaster Fighter giving the option of STR or DEX for their Maneuver DC, making it much easier to play the class however you like.

Also... can't Unarmored Movement already move up vertical surfaces? I know the ability description just says "Across Vertical Surfaces", but I never took that to mean moving Horizontally across vertical surfaces. The idea of being able to kick off of surfaces to change direction seems like something the class is already fully capable of doing. I think it makes it easier to justify if Monks just inherently are able to jump. Right now they need to spend a Step of the Wind to get access to those big acrobatic jumps, which makes them hard to use.

I think just giving Monk's the option to Dash or Disengage as a Bonus Action would allow a lot of the movement features you're requesting. Then using the Step of the Wind feature simply allows you to do both at the same time. And removing the jump boost from Step of the Wind and just making it an always-on feature feels perfectly natural to me.

I absolutely love your idea for disabling strikes, but I don't think it's a good idea to separate it from Flurry of Blows. You're already spending Ki to trigger each strike, and it costs ki for flurry of blows... if a Monk is willing to blow their Ki for that combo, they should be allowed to. I think the only restriction I would give is that a single Monk shouldn't be able to hit a single enemy with multiple debuffs on the same turn. 

Your Deflect Missiles concept feels... clunky. I think just giving Monks the ability to catch magical ranged attacks at an earlier level by itself does plenty.

I also think that, instead of Shatterpoint, which again feels clunky and overcomplicated, you could just give Monks the option to spend Ki in order to give their attacks the Siege function for one turn (which means they deal double damage to objects and structures). A nice representation of stuff like punching through bricks or breaking boards, without adding a lot of weird, complicated rules.

Clarity of Mind also feels awkward to utilize. You talk about it being potentially too strong, but honestly it seems like it would be really hard to use. How often do you finish the adventuring day with full HP? And you lose the bonus as soon as you take damage? Timeless Body sucks and definitely needs something else, but I don't see this as a compelling replacement.

The intention of the unburdened defense was to try and incorporate the concepts of the original rules, but you're totally right, trash it. WOTC screwed up the monk.

If monks are to stand with bards and paladins, they need all the help they can get with their relatively low AC and squishy HP.

So, rather than having to calculate weight, I agree; absolutely monks should get light armor proficiency and you know what? Also gain additional AC with WIS as long as they wear armor that's less than 20 lbs. As a more fragile frontline melee class, they need the extra AC to survive at higher levels, and this would allow them to wear magically light armor and still get the benefits of their WIS modifier in additional AC.

As far as the 'vertical surfaces' thing goes, I've seen multiple sources say that the level 9 unarmored movement absolutely means ACROSS vertical surfaces, NOT up them, which they should be able to do.

A lot of the core rules are very 2-dimensional, they never really go in depth for height. I couldn't find ANY mention in the rules as to how high a character needs to be to avoid being targeted by an attack of opportunity, it's just a horizontal radius, but I figured that as long as you jump higher than the height of an enemy, you should be immune to AOO reactions, and the same goes for jumping.

The rules for jumping are very vague and clunky themselves. For instance, if you have 30 movement speed, you need to spend 10 feet getting a running start to jump your STR in feet, but if you run 20 feet, you're only allowed to jump 10 feet because jumping uses your movement. The intention for the changes (Granted, I probably could have worded it better) was to allow monks to jump their full distance whether they have movement left or not because that's how momentum works.

The expanded deflect missiles is actually just allowing you to apply the Tasha's option for focused aim on a friendly missile that missed its mark, but done using a reaction, so it's beneficial to action economy.

As for disabling strikes,  if I'm honest, I'd rather not put any restrictions on the number of times monks can attempt their disabling strikes, but the new One D&D rules nerfed stunning strikes into the ground by only allowing one attempt per turn, so I tried to split the difference.

I figure, it's always better to buff later than to propose something blatantly overpowered.

Admittedly the shatterpoint ability could use some smoothing over. I just wanted to give both a stealth and smash option, because if a way of shadow monk could do the stealth option, they could poke a hole in a wall, see into the next room, and teleport into a shadow without making a noise. That'd be pretty sweet.

Absolutely though, I think giving monks siege attack properties is both awesome and thematic and simpler than what I came up with.

Clarity of mind is also something I wasn't sure about, if it was too strong. At level 15, there's plenty of options for a monk to heal to max HP after just a short rest if they wanted to, so I thought it wouldn't be out of the question to have the prerequisite of being at max HP in order to gain the +2 proficiency, which is very strong. Probably could just lose the 'bonus lost upon damage' thing for simplicity's sake.

Another option I was thinking about was using ki to bolster an ability score for 1 minute. At level 15, it wouldn't be out of the question, but I hadn't done the math on how much it should cost and how much it should raise, because there's lots of room for that to be super busted.

Thanks also for the feedback. I'll think more about this.

I think the aerial stuff is pretty much solved by allowing Step of the Wind to be free instead of costing ki. I have this homebrew rule in my campaigns and it works fine.

I am also absolutely uninterested in basing things on carry capacity. You will have goliath monk/paladins with Bracers of Ogre Strength running around in plate+WIS AC, which is an even dumber image than the one of the burdened monk you describe (which is also not at all exclusive to monks).

Disabling strikes are interesting, but I don't see how a monk attack is going to result in an INT save. Saves are supposed to match the method of an attack, not the consequence of it. These would all need to be STR, DEX, or CON saves.

I'm not sure what you mean by "+2 proficiency bonus" in Clarity of Mind. You are already getting your full proficiency bonus to saves from Diamond Soul - which is a decent argument against giving monks a further +2 to saves, if that's what you meant. I'm not sure if you've played a high level monk, but I had several fights where the party got beat up pretty badly but thanks to Evasion and Diamond Soul I was completely unscathed. Monk could use some more oomph, I agree with that, but they don't need defensive features. At least not late-game.

Personally I'd like to see more skill utility, but in a different way than rogues. It would be cool for proficiencies like painting or calligraphy to actually do stuff, and for monks to gain abilities that use these tools in a supernatural way. I think that could end up feeling pretty unique while also reinforcing the Eastern aesthetic behind the class.

A lot of monk's defensive issues early game are definitely solved by just providing them with step of the wind for free, definitely. Plus, it means one less thing to spend those all-important early level ki points on.

The idea behind the silencing strike being an INT save is that the throat is actually a pretty hard place to hit because to guard it, all you have to do is put your chin in the way. Striking the throat, whether it be on a humanoid target or not, takes some target manipulation in order to pull off; feinting, deceptive movement like a question mark kick, or conditioning your opponent to respond in one way and doing something unexpected. That's why in self-defense classes, you're taught to attack joints or the groin and eyes over trying to hit the throat, even though it's one of our most vulnerable places.

The clarity of mind feature, as I think more about it, shouldn't really be a core feature. If anything, it would make more sense to a subclass that would do more meditating and be more spiritual than a core class feature.

An ability that allows monks to pump up an ability score temporarily would also be ripe for abuse, so the cost would either have to be pretty significant, especially since cooldowns are something 5e have avoided heavily. It should also be similarly pretty powerful, though, given that it's a level 15 feature.

Thanks also for the feedback, I've got some more thinking to do.