I'm going to provide a somewhat controversial roster. But I will try to explain why I chose some characters.
Bowser Jr.: I don't think Sakurai will simply just throw away old Bowser's moveset, I believe he'll tweak it, give it to Bowser Jr. and give him new moves.
(so that the old moves are torn between Bowser and Bowser Jr.)
Dixie Kong: Tropical Freeze will most likely put her back on the map. And with no K.Rool in sight, I believe Dixie has a slightly clearer shot. (Not to mention she was supposed to be one of the rumored characters to be put in Brawl as well)
Mewtwo: Heavy hints of his return.
Pokemon Trainer: His Pokemon may change, but I think he's definitely coming back.
Ridley: (Though I´m sure a lot of you feel he needs no explanation). Compensation for the horrible treatment Metroid has received as a franchise.
Palutena: Seems to be the 2nd most important character in Kid Icarus. She even got her own OVAs from what I recall.
Dillon: Sakurai is inclined to add new Nintendo franchises, and Dillon seems like a very likely candidate, with a sequel coming out soon (or already out?)
Balloon Fighter: Not only has he gotten PLENTY of cameos, meaning he's important to Nintendo history, but he even got his own segment at Nintendo Land. Not Star Fox, not Fire Emblem.... Balloon Fight got it.
Takamaru: Again, too many cameos to ignore. Captain Rainbow, Samurai Warriors 3, and a whole segment of Nintendoland.
HAL Bailman: My next WTF/Retro combo. Hal Bailman hails from the game Air Fortress, one of (if not) the first games developed by HAL Laboratories. About this astronaut looking dude who rides a jet-bike in space. Then once he reaches a space station (called Air Fortress) he hops off his bike, and uses his Jetpack to move around. Also has a laser blaster in hand to move around. He must destroy a reactor and make it out alive.
Mii: It´s happening. It just is.
New franchises represented: 12.
Thoughts?