If it's crap ... We'll tell you
Crossover games are becoming more and more prevalent (MVC, SSB series, Kingdom Hearts etc). What crossovers do you want to see down the line.
Super Smash Bros. styled Disney fighting game - Wanted one since a kid. Want one now. Of course Disney would never do it cause they're ridiculously protective of their franchises. A man can dream though...
A hack and slash/beat em up game featuring characters from old school Sega games (Streets of Rage, Toe Jam and Earl, Vectorman etc). Sega's got a lot of great franchises that are unfortunately forgotten, something like this would be a great way to introduce them to a new generation.
Super Paper Solid Snake?
Diablovania. I don't know how it works yet, but the word gives me an erection.
Mass Effect and Dragon Age.
I've joked about how Bioware should take all the companions from Mass Effect, Dragon Age, KOTOR, and Baldur's Gate and put them in a fighting game.
Fist full of Boomstick and Skyrim. You start the game with Ash telling how he took out that cocky Dragonborn guy.
World of Pokemon: In my fantasy universe, Blizzard has the rights to Pokemon and is making it into an mmo with the same sort gameplay as the portable games, but majorly overhauled (in terms of graphics and world design) and with an emphasis on online PvP
Now this may sound crazy but how about.... Final Fantasy characters and Disney Characters