We probably talking about more than 5 characters, I could see Crash, Spyro and maybe even guys from Dark Souls and Doom.

I think the OP has a pretty decent hypothesis going. If they pick a Wii character, then it might be "Just Dance" person as an echo fighter for Wii Fit trainer.

Well, I have another theory. We just saw the Belmonts, but Konami has already Snake in the game. So the third parties now can have two representants. Namco so far has Pac-Man, Sega has Sonic and Square has Cloud. Only Capcom has Megaman and Ryu already. So Konami and Capcom have two characters in the game. If you count Bayonetta for Sega, Sega too. So Square and Namco should get a second character, right?

Also, no Doom Marine or Crash or so, it seems Sakurai only speaks with Japanese companies. Ubi is such a long partner for Nintendo, I would've seen Rayman already in the last Smash, but it simply does not happen. No western companies I think.