There really aren't many characters I support, as most of the characters that I've had on a wishlist in the past are already in.
The only 2 I'm really missing are Geno and Phoenix (of course).
The other characters I want are usually either characters that I think should have a new game first, and/or are just vague concepts that I haven't fully thought out yet. Some of them are just characters I like, despite the fact that they have little to no Smash support.
My list:
Ray MK (Would rather have a new Custom Robo game. The Mii Costume is actually REALLY cool, and is one of the few costumes that almost makes up for the absence of a character. But I don't find Mii Gunner fun to play as at all, which is honestly why I'm not super enthusiastic about Geno's costume coming back...)
A new F-Zero character (Would rather have a new F-Zero game first, honestly. Also, most of the F-Zero characters I use aren't that recognizable.)
Paper Mario (Honestly has a fair shot, but I'd rather have a new Paper Mario in lieu of the first two games.)
9-Volt (Vague concept that I haven't really thought of. To be completely honest, I'd take anyone from WarioWare other than Ashley, but I understand she'd be the one they'd go with if they wanted another WarioWare character.)
Ninten (As long as they varied his moveset slightly from Ness and Lucas. Or if they included him as a bonus Echo Fighter, or something.)
Aran Ryan (Veeeeery much a longshot, but he's my favorite Punch-Out!! opponent. He'd also use more than just his fists.)
M. Bison (YES! YES!)