I think jiggs, luigi, c. Falcon, ganon(de-cloned), falco(de-cloned), sheik, mewtwo, game and watch, and marth are all coming back and they will remove all clones (pichu, dr. mario, maybe roy) Ness i dont know and i don't care lucas is good enough for me, if ness is in fine if not oh well.
I also think dixie is in as she is popular, cute, a girl, and will finish the Dk trio, it will take alot more than a trophie in a promotional video to make me think otherwise (If you played Dkc2 or dkc3 you will know the awsome of dixie)
K.rool I think is in too as he is the villian of dk, and ssb needs more villians. I also think DK can pull 4 reps, it was the best game in snes, and still has ok games now.
Olimar is in as he is one of the newest nintendo heroes, and he will be really interest to play as. Ridley is in too, Metriod has only one rep, it needs more and ridley is a perfect candidate.
As for any third party charecter I don't know the list is to big to consider anyone, though I think megaman is in.
In the end none of this matters, sakurai does whatever he whants, it doesnt matter if you can't think of move list for someone, because sakurai, can do it and has, (c.Falcon), and as for size if they are popular enough then sakurai will find a way to put them in, either resizing them or giving them moves, hay Bowser size has always differed to a huge behemoth to the size of mario. The only way we know they are 100% not in is if they are an AT. Anyone else is potential.