I would probably buy it.

Here are things I would hope to see:

Characters from the compilation
Tag teams and combination attacks (based on LIMIT Breaks for most)
"Joke" characters like Dio and Big Bro
Event battles (fighting bosses like Guard Scorpion and summons)
Weird environments like underwater near Emerald Weapon
And, of course, the obligatory alternate outfits (including the Junon Boat and Wall Market events)
Also, Nanaki would absolutely be a participant even if he can only "be fought"

If Zangan were made a character, I would expect he would have the same move set as Tifa. I think that Dyne should be given Barret's moveset (with Molotov Cocktail as a "LIMIT Break" while Barret would keep Catastrophe). Oh, and we have to see Yuffie dressed as a Tonberry again.