I'm really hoping there are new characters added when the wii u one comes out. Honestly I'd even be okay with the wii u version having the characters exclusively for a week or two before they're available on the 3ds to give that much more incentive to buy the wii u one. We were promised the same characters in both versions though, so I'm pretty confident that there won't be wii u exclusive characters.
Honestly though I'll be satisfied with any characters they decide to add, and if they don't add any then... Whatever. Thing is, the one character I wanted more than any other in existence was Bowser Jr. There's no way they could top that when the wii u version comes out for me. Or ever again, really, Bj is my favorite of all Nintendo characters. I mean I'd be pretty excited if they decided to add Vaati, Geno, or Nester, but right now the likely candidates seem to be Ridley, Dixie, Mewtwo, Chorus Men, Bandana Dee (if that's the name), and maybe Impa, and honestly none of those gets my pulse up (though Impa could be fun if she's not a sheik clone). I'd love new characters (I play a lot of MOBAs, we always love new characters) but I if all the new character stuff just turns out to be empty rumors I hope people will remember that we have a pretty awesome roster already. I feel like with Smash Bros method of revealing characters leading up to the game some people have lost all hype for the actual roster by the time the game comes out, cause they've had months to a year to get over it basically. Which means that when the game does finally come out they want something else to be excited over, and that's why rumors start to look so good. Then when they turn out to be false, people claim the game's roster sucks. Smash 4 turned out pretty good I think.