I'm open to a new system, but wouldn't be too disappointed if they used another spell slot system.

The main thing i want are cool, distinctive new 'spells' and features.  I would also like some sort of burn hp for power type system, the type of psionics where you can over do it and start getting nose bleeds until you really hurt yourself.  Levels of exhaustion or other disadvantages could be used as well.

If they design a system for psionic mind battles too that would be a bonus.

They need to design a new system for the people who want it.

They probably won't, but they need to.

That's the thing, Levi.

They don't need to.

If Eberron was any indication (or, indeed, any other sourcebook they print), people will buy the everlovin' shit out of whatever it is they kick out there kinda no matter what.  They can release books like the DMG that're absolutely horrible.  They can release books like Xanathar's Guide that're halfway comprised of reprints from SCAG.  They can release Eberron Rising which is 80% reprint from a book they ALREADY SOLD.

If Wizards releases a book with a new psionic class in it, or even just a batch of vaguely psychic-flavored subclasses?  It'll fly off shelves like it had rocket engines.  They do not at all need to develop a new system of psionic power usage, because people will buy the hell out of whatever slop they deign to dribble out to the masses.  Anyone who thinks different is just gonna do what they want via homebrew anyways, eh?  Why should Wizards bother doing their jobs and designing their own game when the lowest common denominator has the highest total money count and everybody else is "encouraged" to build their own game anyways (except not really, because remember folks: Adventurer's League - the only Real Way to Play D&D(C)).

First off, Rising from the Last War is so much more than a Wayfarer's Guide to Eberron reprint. There is a giant new monsters section, new class, better races, new magic items, and better information on how to create Eberron adventures. It is better than Wayfarer's and is definitely not a reprint. The DMG is lacking, but it is still needed, and useful for new DMs, or at least it was for me. 5e was my first TTRPG ever.

Trust me, if Wizards makes a Mystic/Psion class that is based around the spellcasting system, people will lose their minds, and tell them they have to change it. Also, it would be optional for the people who don't want to complicate their games more. The DM can just say, "I don't know how to do that, and it doesn't work for the game, so sorry, no."

They need to make a new system for those of us who want one, which is quite a bit of us.

I don't really think that what Psionics is and how it is represented should be up for debate. It's been pretty consistent through previous editions. There are six disciplines and each have their own character. The question should really be how do we adapt it to 5th edition D&D.

A quick primer on the six disciplines for the sake of those who are not intimately familiar.

Telepathy is all about the brain stuff. It was where all 5 psionic attack modes lived. Did a lot of things you expected a psychic to do like psychic attacks, inflicting fear and confusion, mind control, charming stuff, and telepathy. Had some real nasty (and fun) stuff too like forcing a target to self harm, switching minds and inserting a mental parasite that would slowly convert the targets personality to yours.

Psychokinesis was straight forward. You projected force with your mind. Was very elementally focused like evocation. Doled out fire, ice, electricity, thunder and force damage in lines, cones and bursts. Manipulated a lot of stuff like the air, sound, light and flames. 2e had powers that manipulated molecular structures.

Psychometabolism was all about the body. Kind of an odd choice, but fits with a mind over matter or reshaping your physical form to fit your mental image of your body. Did things like shape shifting into things with similar mass, growing claws and fangs, enhancing strength and speed, spitting enhanced digestive enzymes, draining the life of your enemies, secreting venom, healing wounds and regenerating limbs, neutralizing poison and disease and even linking with other creatures to transfer wounds to and from oneself.

Psychoportation is about space time stuff. Has had fewer tricks in previous editions. Can mess with time. Can teleport. 2e let you teleport planar creatures to the battlefield that were not under your control, but they dropped this in 3e. Could really use more tricks to bring it up with the other disciplines because the theme is strong.

Clairsentience is the crystal ball psychic. They see distant locations, do object reading and detect things. Plays pretty close to a divination wizard. This would be a good place to stick the Noosphere stuff.

Metacreativity is all about making figments of your mind temporarily physical. Astral Construct is the star of this discipline, giving you a modular creature to summon into battle. Made stuff like walls and force fields. Could manifest armor and weapons too. New kid on the block, as the Discipline was Metapsionics in 2e.

These should be the first six sub classes of the Psion/Mystic. They should focus on adapting these concepts into 5e mechanics before they dip into others.

The only other thing I  feel like commenting on is spell slots vs psi points. Making the psionic class use spell slots to cast would not feel good. Psionics has used a point system since at least 2e. 5e makes you use the spell point system anyway since both Four Element monks and Sorcerer Points both use the point system. It'd be better to have a unique caster that could give people who don't like the spell slot system an option rather than forcing everything to use spell slots.

I don’t think we need a psionic version of every class like 3.5 sorta did, but I think maybe 3 base psionic classes to cover the fighter mage thief styles. To pull names from previous classes.  Battlemind (beefy partial caster, paladin or eldritch knight type thing) psion (full caster) and lurk (sneaky and/or ranged partial caster, in the vein of ranger or arcane trickster.) I think a big issue with the previous mystic was trying to fit all the archetypes in one class.

I think having a psionic subclass for almost every class would be great. Here are some ideas of what each subclass would be like:

• Artificer, we just could have the Archivist, and that would be fine.
• Barbarian, Path of the Raging Soul. When you are raging, an aura of psychic power emits from you, slowing other creatures down, causing disadvantage to attacks, so on. You can eventually add psychic damage to attack rolls, and frighten others with the aura.
• Bard, College of the Singing Psion? Your bardic inspiration grant advantage on any roll that they are applied to. You can manipulate other creature's minds, and have telepathy.
• Cleric. (I can't really see there being a psionic cleric.) Maybe a Mind Domain, but that is a stretch.
• Druid, Circle of the Nature Shifter. You can use psionics to speak mentally with plants around you to manipulate the environment around you, possibly turn into a psionic form similar to the Psionic Wizard.
• Fighter, we already have the Psychic Warrior.
• Monk, we already have the Way of the Astral Self
• Paladin, (again, flavorwise, this would be strange, but I think that the Psychic Warrior Fighter subclass would be better as a paladin subclass.)
• Ranger, Conclave of the Mind Predator, you can hunt psionic creatures with their own powers, you are better at hurting Mind Flayers, Aboleths, Gith, and other psionic creatures.
• Rogue, we already have the Soul Knife.
• Sorcerer, we already have the Aberrant Mind
• Warlock, we already have the Great Old One
• Wizard, we already have the Psionic Wizard.

I think a sorcerer build makes the most sense, but not the Aberrant Mind. If it were a base "psionicist" sorcerous origin, use the DMG's spell point variant rules, and have specific spell lists representing the 6 different disciplines, you would have a pretty solid representation of a true psionicist. 

Now my preferred option would be its own class and not a subclass but not necessarily the mystic. Mystic had some good ideas, but far from a balanced class.      

I personally think that psionics should be represented through spells. Logically, they would scale the same in the end. I think that using Point Casting to "cast spells" is a fine representation of psionics that fits in with the 5e philosophy. I do, however, think that there would need to be other uses for these points, basically giving huge flexibility to the psion.

Psions can be flexible without just using spells. Mystic was a great example of the versatility that comes with a new system. I'm not saying that I liked the Mystic's system, it was broken and bad, but it did have some benefits that can't be replicated through spells. 

I disagree that using the point casting found in the DMG and just letting the psion choose spells would be a good way to represent psionics in 5e. This is oversimplifying the system, and would ruin it. Psionics shouldn't be represented as spells in 5e, I feel like that would be a cheap move, and would make a lot of people angry, as this doesn't fit into Dark Sun, or how Psionics has been in D&D history. 

Psions should have points "psi points" that they use to power their psionic talents/disciplines/powers, but these powers shouldn't be spells, they should be a new system, and the powers scale as you level, instead of just gaining higher level spells.

I think it would work if spells were limited to typical psionic tropes (telepathy, moving objects, precognition etc...) along with "psionic only spells" that other casters can't select. 3.5 Psionics pretty much followed this but added augmentations and scaleability to what were otherwise just powers mimicking spell effects. Its the scaleability that earned psionics a bad rep as being broken and turned a lot of DMs off from allowing them.

Not clear how that wouldn't jive with Dark Sun (being a long time DM of DS since 2e). If spells are more specialized to fit the 6 psionic disciplines and "points" are used to cast/manifest/activate them it captures the same feel IMO. Psionics don't need radical mechanics in order to make it feel different than spells. Its all just thematics. 

If Spellcasting isn't allowed in Dark Sun, how would just reflavoring spells to be psionics be good enough? This would still be spellcasting, just called something different.

 I think this reflavoring would work as a system, but I don't think it would do psionics justice. I want a new system that scales differently than spellcasting, and can do different things than spells.

Most spellcasting in Dark Sun is either via tapping of life force from either plants and sometimes animals (defiling and preserving) or bestowed by some other being (sorcerer-king, elemental plane, or nature itself). A psionicist's power comes from within themselves (mind over body / force of will) and doesn't require an external source to fuel.

Psionics has always just been some form of spellcasting with a different mechanic (accept for maybe 1e psionics). Strip away the need for material components, crazy magic words, finger waving, and grandiose effects, and thats pretty much psionics. Work in some specific psionic only powers or abilities (e.g. maintain concentration on more than one spell) and you have something workable.        

Spellcasting is absolutely allowed in Dark Sun.
(First of all, my idea revolved around psionics being different from spells in flavor, but being mechanically the same, like the artificer, but let's move past that)

Spellcasting in Dark Sun is present. Very present. The only caster that would be affected significantly by being in dark sun would be wizard (although sorcerer might not fit in), because of the lack of latent arcane magic. Magic still exists. Despite gods not existing, divine casters are virtually unaffected. Classes like Druid and Ranger also have casting (and in fact, actually get more spells in some editions). The difference between Dark Sun and other places is that arcane magic is not a free, unlimited source that is everywhere, as it is in other settings. In Dark Sun, for a wizard, with no magic source that they draw from other than themselves, they must either "preserve" or "defile". To preserve is to cast the spell in a careful way that does not drain from other places (not clear on how it works exactly, I'm not an expert on Dark Sun). To defile involves draining the magic from everywhere, and is often much much more powerful. Casting an arcane spell (ESPECIALLY AS A WIZARD) is already a good way to get yourself killed in Dark Sun, but to defile is basically asking every sentient being around you to find, torture, and brutally kill you to make an example to others. Magic is not free (sorcerers might not exist on Dark Sun, due to this). However, there is absolutely spellcasting.

Quote from LeviRocks >>

If Spellcasting isn't allowed in Dark Sun, how would just reflavoring spells to be psionics be good enough? This would still be spellcasting, just called something different.

 I think this reflavoring would work as a system, but I don't think it would do psionics justice. I want a new system that scales differently than spellcasting, and can do different things than spells.

 ^^^This, all of the this.^^^

And yes, Psionics, at it's core, is another form of magic. If that form of magic is represented through spells, but using point casting instead of slots, I would be satisfied (as long as they converted the classic psionics stuff into these spells, and had some of them be Psion only). 

Either it scales with spellcasting, or it is broken as ****.

The entire game is balanced around spellcasting.
Wait, by "scales differently", do you mean like through upcasting? Cause that is something I would agree with, but they should be spells with different effects at different levels, not their own, separate but actually virtually identical except these minor differences, system.

I will never be satisfied with Psionic powers being spells. I will rail against it until I am blue in the face. If that is how it gets officially released, that book will be banned at my table.

Concept for Psionics:

Schmeills:

basically the same rules as spellcasting, with a ton of bloated, effectively reprinted options, but it has a different name, and is therefore valid. 

Quote from Bunsenburner03 >>

Concept for Psionics:

Schmeills:

basically the same rules as spellcasting, with a ton of bloated, effectively reprinted options, but it has a different name, and is therefore valid. 

 Why should any of that have to be true?