I think anoher pokemon trainer'd be cool, like another region's trainer.
So people can do pokemon battles XD
Also I always wanted Paper Mario in super smash bros =)
He always has a lot of usable attacks, and they can do pretty much anything as his final smash.(ie: giant retro mario)
Paper Luigi should go too ;D
Maybe some more uniqueness between characters and "clone" characters.
Like making toon link a little more different than regular link, and stuff like that.
Oh and last but not least, Tingle should be a character!
he's my favorite Zelda character.