The Kirby GC-game that is now meant for Wii will probably be released eventually. I'm expecting atleast Kirby and Dedede in it, and possibly Metaknight.
Star Fox will come for Wii sooner or later. Fox, Falco and Wolf are shoe-ins.
I don't think Nintendo will pass up on a F-Zero for Wii. Captain Falcon will return.
Olimar is all but confirmed. I will be extremely surprised if Pikmin 3 does not feature Olimar.
Pokémon trainer should count, since I believe Ivysaur, Charizard and Squirtle are in the Pokémon Wii game, aren't they?
Also, I believe in the Kid Icarus Wii-game, although that's just my personal belief.
EDIT: Some people seem to be misunderstanding the thread. From what I understand, the OP is not asking what characters will return in a Smash Bros. 4, but rather what characters will be featured on the Wii in a game of their own series.
