The number 1 thing I want to see improve is…
… for the game to just feel more fluid. For instance you initiate a wild encounter, maybe a ! appears and the corners of the screen highlight to indicate battle mode. Pokémon appears instantly by your side to battle.
But you can press B to instantly flee. Basically things should feel more ‘on the spot’ rather than a transition to where you as the player repositions and you get taken away from your spot.
If your avatar is standing too awkwardly close to the Pokémon, your avatar can just auto move back to make some distance while your Pokémon are battling with each other.
Trainer battles on the other hand should work like in Champions, maybe even with the full animations, since I think battles are more of a spectacle.