Oddly, I was thinking of a few old characters that I've always thought ought to be honored with a spot in a Smash Bros. game:
Pacman - One of the oldest game characters, right up there in the venerable ranks of the Pong paddle and such. I'm thinking Super Pacman style too, rather than the old-school 2D pizza-shaped pacman, the one with eyes and a cape and all. Final Smash being the power pill, where everyone goes all "blue ghost" (looses the ability to attack for the duration of the smash, and their appearance changes to monochrome blue with white eyespots)
Megaman - Old-school, or X style. With all the different mega man powers through the years, Im thinking the ability to swap between suit-types and the plain B attack changing accordingly. As for a Final Smash, something along the lines of calling in Rush as a secondary fighter, or to bomb the heck out of the stage.
Chrono - They seem to have avoided RPG characters so far (unless you count FE), but Chrono is so nearly a fighting game character already, he would work well (not to mention, with the addition to the SSB lineup, Development of Chrono Break might be able to continue again). As far as a final smash, possibly calling in a cameo combo with other characters, or just Luminare.
Black Mage/Vivi - FF needs a representation in Smash Bros. being one of the oldest and largest RPG franchises that Nintendo ever started, and Vivi is one of the few developed characters that hearkens back to the very beginning of the series, yet is a developed character. for a Final Smash, I'm thinking Trance Mode MagicX for Vivi, or in the case of the Black Mage, Ultima.
P.S. ...and like parasols to simulate Peach's moves, Excitebikes should definitely be an item to simulate Wario's bike. Not to mention it'd be flipping sweet to mow people down with a piece of ancient Nintendo history.