They could also do a prequel to WFC. Deal with the start of the war, the rise of Prime and Megatron, that sort of thing.

Personally, I'd rather see a sequel with some lost-in-space action before reaching Earth, maybe interspersed with a few levels of Tets' idea about checking out the survivors on Cybertron. It'd flesh out the games and get a bit more mileage out of the Cybertronian design style.