Let's talk about features. Old ones, good ones, bad ones, and ideas for new ones.
Natures were just very poorly implemented, and made catching new Pokemon for battle purposes almost as tedious as breeding for IVs.
Instead of IVs and Natures, I'd rather just have Additive EVs (normal EVs) and Multiplier EVs; Multiplier EVs being LIKE Natures, but you could perhaps distribute percentile increases/decreases as you please, with the per-stat cap being greater than 10%, and the ability to affect more than two stats. For example: +50% Attack, -25% Special Attack, and -25% Speed.
Now, before you say that would be broken, I must refute you by saying that it wouldn't break anything, it would simply reshape the metagame. And while I think +50% is fine, we could perhaps cap it at +25% and -50%.
I'd also like a system that allows numerous slots for more Abilities, Moves, and Items. This might help balance out weaker monsters --- for instance, a Charmander might have 2 more Ability slots than a Charizard.
We could also have a Genetics system that allows Abilities to be passed to Pokemon that don't have them, as well as Passive Abilities like how a Pikachu benefits from a Light Ball.
Again, this wouldn't be broken at all --- it would simply shift the metagame, increase the game's complexity, and perhaps call for a few limitations for certain monsters for balance sake. Like, Speed Boost, for instance, might require 3 Ability Slots, and be incompatible with certain genes (and therefore certain Pokemon, items, and other abilities).
Pic unrelated. I'm a FUCKING mobile poster and thus have few pictures.
Furthermore, maybe on top of, of aside from, Multiplier EVs, we could have Additive Stat Trade-offs; ie, trade -50 Speed for +50 Attack. Additive instead of percentile trade-offs.