I wish I could say that I could definitely see Square adding in some sort of costume-swap mechanic (mind you, one that doesn't change stats), but I can't. I've been burned by them too many times to believe they'll do anything more than directly translate VII to a PS4 graphics engine with the lowest amount of work necessary.
It'd work, though; everyone in the cast has at least one different possible outfit;
Cloud has his babby Cloud look from Crisis Core, his babby look from FF7 itself, his Shinra Grunt outfit from the battle inside the Nibelheim Reactor, Drag Cloud, the sailor outfit from the boat ride to CdS, Kingdom Hearts Cloud, and his morose motherfucker look from Advent Children.
Aerith has her Crisis Core look in the sundress, her Corneo-bait dress, and her sailor outfit.
Barrett has his Corel clothes (which are admittedly his default outfit except with a white undershirt). his sailor outfit, and his Advent Children look.
Tifa has her babby dress from the flashbacks, her Corneo-bait dress, her cowboy outfit, her sailor outfit, and her Advent Children giant giant-boob-shielding leather apron.
Red's a little tougher; but I suppose you could go with normal, sailor suit, and a Seto skin?
Cait Sith has a few interesting options; there's the normal version, where he rides the fat Moogle; there's Cait riding Red XIII, as in Advent Children; and if you wanna acknowledge Dirge of Cerberus, we could always have the wonderful bit of inception that was a robotic Reeve being piloted by Cait Sith, itself a robot being piloted by the real Reeve.
Yuffie has her 'defender of Wutai' outfit from Crisis Core, a sailor suit, her Advent Children look with the vest, and her Dirge of Cerberus outfit.
Vincent, obviously, has his Turks suit. And that's about it, really. He's recruited too late to be a sailor like everyone else.