Quite simple, would you buy it? I would if its anything like CvsT haha.
If such a game would exist, the roster must be like this:
Mario, Luigi, Peach, Bowser, Link, Mewtwo, (a pokemon), Captain Falcon, Fox, Ness.
Ryu, Ken, Chun-li, Bison, Viewtifl Joe, Megaman, (someone from darkstalkers), and 3 other people.
Since CvsT will be the latest game for a while, its just wishful thinking that capcom would make another crossover game.