NOt sure what other Alt mode BB would be. At this point, he looks best as a Camaro. Not even his orignal Bettle alt mode works and if they did decide to do this, it would be more of a down grade.
Prime could pull off an International Lonestar semi truck..
For the wreakers, change them to battle version Baja trucks instead of battle version Nascars. Have Sideswipe a ZR1 Corvette, Dino stays as a Ferrari 458 Italia, but give him a few upgrades like wheels, Black roof ETC.
There are plenty of alt modes i like to see in the next movie..
If hound makes an apearance I'd like to see him as a military Jeep and Trailbreaker as a raptor F-150 truck.