Out:
R.O.B
I still don't get what's the deal with this guy. So many other characters fans where expecting for this Smash and Nintendo come up with this. Sure, he made a nice Subspace Emissary character, but he is not as nearly atractive as a playable fighter.
Olimar
This guy barely fights, the Pikmin do all the dirty job for him! I played Pikmin and could never expect the fragile little Olimar would have been made a fighter.
In:
Roy
If he was to make it trough, he could have been a nice semiclone from Marth. He sure is going to be missed.
Characters from Golden Sun
Goulden Sun is a very famous game with a solid fanbase, the various techniques and spells from the game could have been implemented easely, Issac, Felix and Garet all have potencial for being smashers. The reasons why Nintendo only came up with a Issac assistant trophy are still a Mystery;
Baby Mario and Baby Luigi
The two would be a nice alternative for smaller and faster Ice Climbers; Of course, they should have their own move set and no baby should have been sacrificed for the recovery of the other. But I can imagine why Nintendo hasn't implemented them, babies flying around and engaging in mortal combats could damage the image of the game;
Megaman
This one has great potential as well.I would prefer the implemention of the Megaman from "Megaman 64" (know as well as Megaman Legends for PS1) as the appearence in SSBB could icentive Capcom to release a sequence for the classic;
Leon S. Kennedy
Surely Nintendo would have to come up with a moveset for him, but i would have been worth the trouble since his I very famous among the GC and Wii players (I would love using his tornado kick!);
Soma Cruz
I believe Soma was the only character to take the main hole in two Castlevanias on a row, and both great hits for Nintendo portable consoles. His insane moveset could give many options for his character design in Brawl;
Banjo-Kazooie
Nothing whould better reresent the service this couple have made for the the owners of N64. Sadly, Microsoft whould never alow it. You know, it's just business;
Mii
This character would surely make a great addition. Fully customizable, every Mii fighter would be unique.
I really hope Nintendo will someday start adding downloadable content for their games, so maybe SSBB is going to see some new faces in the future.