Meta: Final Fantasy crossover possibilities

Dissidia is Crossover Crack, but I haven't yet played it. However, even without Dissidia as an excuse, there's a lot of Final Fantasy characters who could collide in intriguing ways with minimal fiddling. Sev and Rina's playthrough of ALL THE FINAL FANTASY games in moogle_university has gotten me thinking about various possibilities.

( Meta babbling about likely crossover candidates )