I hope they...
remove tripping, or make it optional and off by default if people actually think its a good mechanic (for some random reason)
Definitely fix clones, there should be 0 clones in this game, which probably means there can only be 1 link but thats fine with me because i never cared for toon link. Definitely want to see Ganon make it in this game but with a completely remade moveset (the sword he took in twilight princess would be awesome, or some dark magic hand blasts, or both!)
someone mentioned the removal of jigglypuff, that will never happen, jigglypuff has been in every smash game and already has a well established move-set, plus its hilarious.
Pokemon trainer can stay, but bring new pokemon. As much as I miss mewtwo they should stick with the pikachu/jigglypuff/new gen bipedal badass pokemon trio
as some people have mentioned Marth will probably continue to be the face of fire emblem, so I think he should get a more rugged counterpart, Ike was pretty decent and should be treated as the baseline, a heavy bruiser type.
The mario and co roster is big enough as is, nobody should get cut but nothing else should be added.
I don't think Sonic will make a comeback but it wouldnt bother me if he did, but should suck less (and if we go in that direction, I'd like shadow as his COUNTERPART, not clone!)
From Starfox, Crystal would be ok...i guess. But I think they should add or remove one to either make it a duo or a full team of four. Considering Falco has been in 2 games, he could probably stick around provided he loses his clone status fully, otherwise keep wolf and remove falco.
Definitely keep the Zero Suit Mechanic, she was a character of her own without "increasing" the roster.
Ness is enough to represent a relatively small and less known series like earthbound, so Lucas can go.