I would like for all of the currently known Keyblade wielders to be playable at some point. Have a battle system like FFX had; where you can change your party members during battle.
I didn't buy one at first because it was expensive and there were no good games on it. Then when XIII and later XIII-2 came out I reconsidered buying a PS3, but changed my mind. I have to buy one now, for KH:ReMIX. NO EXCEPTIONS.