OK ok, this is a long topic, and I dident read all of it, so forgive me if what I will say has been touched on already.
I see we are currently discussing MegaMan. He was one of the first 3rd party characters I would want to see in SSB:B. I think they should either use the classic
NES Megaman or
Megaman X without armor upgrades. As far as a move set goes, I think it would be really cool to have Megaman use his Kirby-like ability to copy powers. Megaman's color would change accordingly, just as he did in his own games. Copy Link, and get some kind of arrow or boomerang shot, copy Pikachu and have an electrical shot, and so on. Try as much as possibly to disgunish him away from Kirby, so that, if Kirby recived Boomerang from Link, Megaman would recive Arrow Shot. And, just as in the the classic games, you would have to beat the character to recive their powers. Such as. When you start each match as normal Megaman, both A and B would would do the same Mega Buster. But each time you defeat a player using the B move, their power is added to your abilities. Every time you defeat a diffrent character using B you gain thier power and rather than replacing the old one, like Kirby, you keep it and can cycle between them, but you loose all the powers you have gained each time you die.
Yeah, I'm bored so I'm just randomly coming up with stuff.
As far as other 3rd parties go, I think Japanese 3rd parties have the more likley chance to have their characters added.
Sega - Sonic
Capcom - Megaman
Konami - Solid Snake & Simon Belmont
Squarenix - Cloud
Hudson Soft - Bomberman (I cant see him as the best character, but it is possible considering the Virtual Consoled deal between them an Nintendo)
Namco Bandai -
sombody from Soul Calibur maybe? Pac-man? lol
SNK - Metal Slug and King of Fighters are the only notable games I can think of...
Taito - Bub and Bob???