I wouldn't mind if Link, Zelda, Sheik and Ganondorf were given their Ocarina of Time looks (and voices in Link and Ganondorf's cases) as DLC. Same thing for Marth, Roy and Ike with their respective costumes from FE3, FE6 and FE9, similar to their previous appearances in Smash. They could easily be labelled as "Classic costumes" or something similar.
Probably not gonna happen, but would be a nice addition.
Well, it's already good enough that this game already brought a lot of alternate costumes:
- Little Mac's Wire Frame model and hoodie
- Zero Suit Samus and Shulk's fanservice costumes (counting as both kinds considering they come from their own games)
- Wario's classic overalls (also in Brawl)
- gender options for Villager, Wii Fit Trainer and Robin
- alternate characters with Alph (for Olimar) and the Koopalings (for Bowser Jr.)
- Cloud's Advent Children outfit
That's far more than what previous Smash Bros. games did. Brawl only had Wario getting this treatment.
And let's not forget that Pikachu, Jigglypuff and Pichu were actually the first characters to have costumes instead of just color/texture swaps.