I want more human like characters like Samus, Cap, Snake, etc. I like how they contrast from the more cartoony characters.
^ Both in regards to balance issues, and for Ninty to program said moves.
At most, I'd say being able to choose among B moves. This could actually be pretty interesting, since an alternate Up B might give characters like Bowser or DK vertical recovery. I'd certainly prefer a move like DK's Giant Punch over Ganon's Warlock Pawnch...