But but... I have Woodgreen and that's a massive crossover XD (granted AU).

It depends on the worlds crossing over, imo. As long as the writer can make sense out of how the hell those two worlds manage to cross, and give me this 3rd world in which those 2 exist in a seamless thread, I'm all over it.

Case in point, my secret obsession to Heero/Usagi XD was and will likely always be the pairing people will question my sanity for.