Freely mixing and matching classes and subclasses

[Lvl 2 Expert]

I just had a stupid idea, but the fun kind of stupid. I'm sure others have had it before, there probably have been threads about it, and hopefully a few people have even playtested it already.

The idea is, that in the big grey area somewhere between multiclassing and gestalts, you could have classes that freely pick their subclass from any class. A Champion Barbarian that uses maneuvers while raging, an Eldritch Knight Ranger that can cast a cantrip and attack in the same action while hunter's mark is up, a two level Warlock dip that gains the improved initiative and protective features of the War Wizard. If both the class and the subclass give spellcasting you are treated as a multiclassed caster, as far as that makes sense. If the subclass has features based on your class level the new base class is used for that. If the subclass relies on some sort of feature or point supply from the original parent class they're probably skid out of luck.

So, this obviously opens up lots of possibilities, and some of those possibilities are bound to be broken. Which subclasses do you feel add the most to a character, and what would be the ultimate class to use them on? Is there a possibility out there to make a monk that doesn't suck? Is there a craaaaaaazy race/class/subclass/3 feats and a hat combo out there that breaks the game by level 6? And most importantly: do you feel like it would make thematic sense? Because I can sort of see it. A Barbarian with a dash of Circle of Dreams Druid to emphasize their peaceful side, a snooty Wizard with assassination as a hobby. A warlock with a patron that grants an animal companion??? That would be kind of cool...

Any thoughts?

[Chronos]

If both the class and the subclass give spellcasting you are treated as a multiclassed caster, as far as that makes sense.
So if a paladin takes eldritch knight, they're now a 5/6 caster? And a wizard eldritch knight is a 1 1/3 caster?

And of course there's the problem that some classes rely more on their subclasses than others. "One subclass worth of abilities" isn't always the same amount of abilities.

[cutlery]

And of course there's the problem that some classes rely more on their subclasses than others. "One subclass worth of abilities" isn't always the same amount of abilities.

This is the biggest issue; they also get abilities at different points due to how the base class is structured.

[Hellpyre]

And several subclass abilities reference abilities of the base class - are they unusable or do you also inherit any referenced abilities? Overall, I think it's really an unworkable idea.

(That being said, an Ancients Paladin subclass progression on something that doesn't use its native subclass too much would add wonderful tankiness.)

[TyGuy]

I was just thinking about this early today. But I was thinking that it would stay within the same class. And maybe some restrictions on multi level features. Could get complicated very quickly because of features like spellcasting on 1/3 casters and features like storm herald's that all key off the first pick.