Other than being property of Capcom, that is a good idea. After I played melee for a while, I, too, felt like there should be more characters, but if you really think about it there are no others. Kid Icarus is often mentioned as a wanted addition, but I've never played his game(s), so I don't know. If you look through all your trophies, other than more Pokemon, it seems that Nintendo has no one else.
So an alternate solution is letting existing "clone" characters play differently or better yet having Nintendo make more franchises.
(Seriously the main reason I want new franchises is for Smash Brothers, which if you think about it- it is preposterous...lol)