i'm in your conscience
I don't see any reason why gen 6 wouldn't be able to trade or migrate with V. I don't think they'll be making any major changes to the IV/EV or nature system, which is why we can't trade/migrate from gen I and I to anything III and beyond.
I'm hoping we can trade instead of migrate. There was no reason that gen IV and V couldn't trade honestly, and that migrating game was awful. Just let us trade and keep it simple. Of course, following gen I and II trading rules by no new Pokemon or moves or items. Not hard, really.