I'd like to see Riku as a playable character...Well, it already happened in CoM, but now you would be able to alternate between him and Sora at a save point or something...Imagine both fighting together, along with that other kid holding a keyblade in the E3 trailer? Wow...
Storyline-wise, I'd like to see Sora kicking Ansem's butt once and for all. I'm sorry for you Ansem lovers, but if he could only appear as a spirit or something, it would be way better than having to fight him over and over...How about a new enemy, CONTROLLED by him, BUT not him?