Well, it got me to ask what do you think? Megatron was given a choice of decepticons to free up and join him. He picks five rather than four in the movie. Since Onslaught was already chosen, he will also select the movie representations of Vortex, Swindle, Blast-Off (Or maybe Nitro could take this since it's too much size discrepancy for a space shuttle to be a part of the team) and lastly, another tank character since brawl was already killed in the first film. In a plot twist, no one from TRF, or Earth for that matter, knew that the five specifically selected decepticons can combine and form Bruticus. It is all part of Megatron's master plan. Do you think it would somehow be a good fit? Maybe perhaps using this to battle the knights rather than Infernicus. Of course, putting up a much better fight and not be decapitated in one swing by Prime.
I like the idea of the Combaticons being in the movies. We could get some cool toys from it. Unfortunately this is what would eventually happen to them after he blasted their combiner mode apart.
Your idea alone, is much better than what the entire Writer's Room came up with. I would have absolutely loved that.