I can't say much for SMT (my roommate is a big fan, but I haven't played any) but I assume the game will be a tactical RPG like FE, I can't imagine it working well in another context. As for the game itself, I got nothing. I thought Pokemon Conquest was already an absurd enough crossover, but it isn't too farfetch'd (ba dum tiss) to imagine Pokemon existing in other time periods and settings. SMT and FE are so wildly distant and specific to their own settings that I have no idea how they'll bridge the gap. My guess would be more time travel like in Awakening, but even then it still sounds pretty wacky.
Here's where I would write something I think is witty at the time, and later realize I'm an ass.