Stating the obvious here, but with Unicron in the T6 storyline, that means Primus will also be a part of said storyline. Before anyone says it, Primus was not Cybertron. If he had been, it would have been as strongly hinted at, as Unicron being Earth. My guess, is that they'll probably use a different planet (maybe Caminus?) for Primus, or have him hiding in a character who has no idea that they're a vessel.