Well, i'd like to think the writers learnt their lesson in Johto and will correct their mistake this time. I'm not talking every single Unova Pokemon either, and they don't have to be used frequently over and over, it can be minor so that the Gen 6 Pokemon get their fare share. On top of that, I have no objection of the Unova Pokemon gradually disappearing having reasons to return to the lab, or making space for new Pokemon.
Eh, just trying to make a joke out of it XD
"I already told you, I don't mind playing the bad guy every once in a while."~ Sonic the Hedgehog