On the concept art I saw back in January, he looked as though he had a movie head on a G1 body. I don't know if that made it into the final cut but judging by the info which came out of SDCC, it seems as though it did. My fellow staffer Red Goblin saw it too so he made an artwork out of the concept: Prime's new design based on everything I know
Time will tell I guess. I just find it hard to believe that's Optimus. It's like they're not an advanced complex alien race anymore.