I'm hoping that difficulty levels return (and without the bullshit that required you to beat the game and then share it). I really liked playing Challenge Mode on B2W2, even if it wasn't that challenging, the increase in levels and such was better than regular.
Also it would be neat if they allowed a feature where, at the beginning of the game, you get to choose whether you want to play the entire game in Standard (which would include all battle types as the last few games have done), Single, Double, Triple, Rotation
(maybe even Horde?), or some variation on that. So depending on what you choose it will change how battles will be played all the way through the game. I know Single is what most consider the "main" battle style, but the other styles don't seem to get much attention unless you play in the Subway or Battle Tower. Just something I'd personally like to see included.