I have seen it suggested by others that some classes (if not all) could benefit from having a secondary customization option beyond the subclass, similar to how Warlocks have four Pact options and unique invocations to help customize them further. That has me thinking, what would this secondary option potentially look like for each class? I wanted to make this thread to share my own ideas and hear others. 

1. Wizards - Schools of Magic

I think one application of this idea would be to remove the schools of magic as subclass options and turn them into a sort of "study focus" for a wizard. So you could have two Bladesingers, but one focuses on Abjuration while another focuses on Illusion magic. Each school could have unique "invocations" based around reworking the old subclass features as well as introducing some new ones. 

2. Fighters - Fighting Style & Maneuvers

Alot of people have been hoping that maneuvers would be expanded to become a general mechanic for fighters, if not martials as a whole. In this way, I could see a fighter's chosen fighting style unlocking unique maneuver options. In this way, every fighting style would be tied to some number of unique maneuvers, with the Battle Master being allowed to pick from any regardless of their fighting style. 

What thoughts do you have? 

Quote from Kaboom979>>

1. Wizards - Schools of Magic

I like the idea of moving the schools of magic to a "school" option to pick which school you can copy into your spellbook more easily, plus maybe one or two other benefits later, but I wouldn't expand it too far beyond that. Warlock invocations/pacts compensate for a Warlock's limited spellcasting due to their small number of pact slots, whereas Wizards are already very versatile thanks to their spells.

I do think they need to focus on Wizard sub-classes that change how Wizards play in more interesting ways (like Bladesinger); while some of the school-specific sub-classes are okay, it's just kind of boring to structure them this way. This would also allow Wizards to represent all of the schools in the new PHB without having to re-publish 8 sub-classes.

I think Cleric should gain something similar to represent all of the major domains of deity (death, life, light etc.) for the same reason. Let us pick the deity we follow, then specialise in how we represent them.

2. Fighters - Fighting Style & Maneuvers

I do agree that fighters could really benefit from having manoeuvres as standard, as it gives them a core resource to play with as well as some much needed basic versatility.

This could also allow for fighting styles to be expanded out to Barbarian and Monk who could do with the buff (and incentive to use different weapon combos). Not sure I'd keep the Battle Master in this case as I don't think "core Fighter but more" is terribly interesting.

I'd probably also discontinue Cavalier, and instead turn mounted combat into a fighting style with unique manoeuvres for a Fighter (or Martial Adept) to benefit from. Maybe do the same with support abilities of Cavalier and Purple Dragon Knight (e.g- tie those to the protection fighting style)?

3. Druid 

A - Wildshape

This idea would require some heavy redesign of certain subclasses, but the idea would be that each Druid could choose what they want their wildshape mechanic to do and gain certain improvements as they level up. So some druids could transform into beasts, others could summon animal companions, others could perhaps enter some special state with enhanced connection to nature (i.e Symbiotic Entity or Starry Form) and so on. 

Just to spitball some ideas ->  Wildshape Options:  Shapechange (traditional Wildshape), Wild Companion (Tasha's Optional Wildshape), Channel Nature (could start out as something similar to Agonizing Blast or Potent Cantrips, allowing you to add your Wisdom modifier to damage from Druid cantrips). 

Circle of the Land, Circle of the Shepard, and Circle of Dreams would basically be unchanged, but the other subclasses would need to be reworked since their main thing is modifying Wildshape

B - Terrain

This idea I saw suggested elsewhere and is similar to dropping the school-based subclasses from Wizard. Just remove the Circle of the Land subclass and let every druid have a focused terrain, which unlocks certain spells as the primary benefit and could grant additional benefits based on the themes surrounding the chosen terrain type. 
Could arguably do something similar to Rangers, especially with the newest iteration formally moving away from things like Favored Terrain. 

4. Sorcerer - Spellcasting Ability

Okay, this is a weird idea, but hear me out. The idea would be to make Sorcerers one of the most flexible casting types by letting them choose what their primary casting ability is going to be. The flavor and theme of it would be to reflect what connection allows them to draw upon their natural magical abilities. It might look something like: Psionic (Int), Practice (Wis), or Willpower (Cha). You could even introduce something like Blood and allow for Con-based casters as an option. 

The obvious implication of this would be that Sorcerers would also become very popular multiclass choices for other casters and half-casters. To avoid this, youd maybe need to make the "primary benefit" at 1st level just be the choice of spellcasting ability and lock the other, more interesting power-ups behind higher levels to make 1 or 2 level dips less appealing. 

Quote from Kaboom979 >> 

The obvious implication of this would be that Sorcerers would also become very popular multiclass choices for other casters and half-casters. To avoid this, youd maybe need to make the "primary benefit" at 1st level just be the choice of spellcasting ability and lock the other, more interesting power-ups behind higher levels to make 1 or 2 level dips less appealing. 

 Or what you could do is to only lock them if you take sorcerer via multiclassing, not as your starting class.

Also, it’s interesting to see someone else suggest a flexible spellcasting stat, since I’m currently working on a class that gets to choose its spellcasting ability. And actually, it has invocation-like abilities, and the option to get of some of them will be dependent on your choice.

I just had another idea, this time for Barbarians: what if everyone got totems instead of Totem barb being its own subclass? This would obviously call for a nerf of some of the abilities (looking at you, 3rd level bear totem), but what if every Barbarian had access to an "animalistic" or "ancestral" totem? This would allow the Barbarian to get some smaller buffs and changes (like the Eagle totems sight or the Wolf totem's improved tracking) that could benefit the player's desired style. This would also open up the possibility that in future books they could release additional totem options (based on other animals, monsters, or even general heroic figures) that would add to the customization without it defining the entire subclass. 

I dont think that the loss of Totem Barb as a subclass would be too great of a blow. It feels to me like only a handful of options get picked anyway, since your choice defines your entire subclass power, and youd want to make the best choices. With weaker abilities tied to totems, players could play around with ones that maybe synergize with their chosen subclass or just fits the flavor of their character without worrying about it costing them too much mechanically 

Quote from Kaboom979 >>

2. Fighters - Fighting Style & Maneuvers

Alot of people have been hoping that maneuvers would be expanded to become a general mechanic for fighters, if not martials as a whole. In this way, I could see a fighter's chosen fighting style unlocking unique maneuver options. In this way, every fighting style would be tied to some number of unique maneuvers, with the Battle Master being allowed to pick from any regardless of their fighting style. 

 One issue I could see arising from this is that if maneuvers were based on fighting style, you would expect them to incorporate that fighting style into the maneuvers. For instance, maneuvers gained from the unarmed fighting style would focus around having a free hand, protection maneuvers would be centered around use of a shield, etc. This greater specialization would make it hard for a battlemaster to leverage their flexibility without also having some kind of ability to juggle their weapons/shield around. Alternately, keeping the maneuvers generic is going to make them feel kind of arbitrary as to which fighting styles they belong to.

In short, fighting styles tend to be centered around a particular build - sword & board, great weapon, throwing, twf, etc. while maneuvers are generally designed to not be build-specific so that a battlemaster can more easily mix and match them.

Quote from scatterbraind >>

Quote from Kaboom979 >>

2. Fighters - Fighting Style & Maneuvers

Alot of people have been hoping that maneuvers would be expanded to become a general mechanic for fighters, if not martials as a whole. In this way, I could see a fighter's chosen fighting style unlocking unique maneuver options. In this way, every fighting style would be tied to some number of unique maneuvers, with the Battle Master being allowed to pick from any regardless of their fighting style. 

 One issue I could see arising from this is that if maneuvers were based on fighting style, you would expect them to incorporate that fighting style into the maneuvers. For instance, maneuvers gained from the unarmed fighting style would focus around having a free hand, protection maneuvers would be centered around use of a shield, etc. This greater specialization would make it hard for a battlemaster to leverage their flexibility without also having some kind of ability to juggle their weapons/shield around. Alternately, keeping the maneuvers generic is going to make them feel kind of arbitrary as to which fighting styles they belong to.

In short, fighting styles tend to be centered around a particular build - sword & board, great weapon, throwing, twf, etc. while maneuvers are generally designed to not be build-specific so that a battlemaster can more easily mix and match them.

 Thats a good point. I think that if maneuvers became a general fighter feature they would need to make some slight reworks to Battlemaster anyway, so I could see adding some ability that allows them to "juggle" weapons around more efficiently like you said or maybe even just allow them to ignore weapon-based restrictions for maneuvers (although this could get a little wonky for some of them)