As a joke I once said that the best way they could do a Pokemon/MegaTen crossover would be if a demon invasion happened in the Pokemon world so that all humans were wiped out and then the demons just became Pokemon trainers. You play as Jack Frost, your rival is Pyro Jack, and we even started planning out who would be the gym leaders and what type they would use (Ukobach being the fire gym at the starter, later gyms being like Thor with electric types)
It started as a joke, but truth be told I kinda want to play that now. --- Don't forget to check out my MegaTen themed webcomics at http://www.drunkduck.com/user/Strain42/ (Currently Updating: Persona 4TW Add-On M-F)
Plus, when was the last time a main series game crossed over with another series EVER Really. --- Anatidaephobia is the fear that somewhere, somehow, a duck is watching you, staring into your soul, using its duckiness. QUACK.