You're thinking this wrong.
A crossover game should have tons of series, and in order to make this fesible, you have to only pick one or two from each series.
Take this idea. Two separate fighting games with the same mechanics, one following a 50 character roster of gaming characters (good/evil division so 25 playable series characters) and another that acts as a clash of east and west, comic books versus anime and manga, throw in some tosaku and other stuff.
Where things get cool is there's an ongoing story with each game, each getting two DLC packs with more characters later on that each continue the story. The last DLC Pack combines the two games for the big finale with the last few characters. For the Hell of it, add it support characters so you can pack in even more.