With the news that TF4 is "a whole new re imagining of Transformers", there's a chance they might overhaul all the characters to be completely different from the current movies and maybe even replace BB as the "main Autobot". And honestly, I think it could be Ratchet. Think about it, next to BB and Optimus, he's the only other constant for the Autobots core group. He was in the movies already, in Animated, and WFC, and Prime. Characters like Jazz and Ironhide get replaced with the likes of Prowl, Arcee and Bulkhead, but Ratchet always manages to stay. I think back to Infiltration where Ratchet was the star, and I think the very nature of the character makes for great entertainment.