There are hundreds of characters I'd want to see in the next Smash Bros, but I'm gonna list the ones that have at least the slightest chance of being included.
-Travis Touchdown (Suda51 has already mentioned he'd want Travis in the next Smash Bros.)
-Little Mac (Now that Punch-Out!! is out, Lil' Mac's popularity has increased enough to include him as a playable character.)
-Gengar (He's awesome.)
-Ganondorf with a new move-set (Don't tell he wouldn't be awesome swinging his sword around like a lunatic.)
-Mega Man (They let Sonic in because of the whiny fans. Why not Mega Man?)
-Bowser Jr. (He might actually have a interesting move-set, kinda like a mix between Diddy Kong, Bowser and Mario.)
-King K. Rool (He's even more awesome than Gengar.)
-Simon Belmont (He is f***ing Simon Belmont!)
-Gray Fox (1 word: NINJA!)
-Zero (Imagine Ike a little faster, lighter and wielding a goddamn lightsaber!)
-Wolf Link (Not a separate character, more like Sheik or Zero Suit Samus.)
-Pokemon Trainer (Except that this time the characters aren't Squirtle, Ivysaur and Charizard. They're Bulbasaur, Charmeleon and Blastoise.)