The EPA can suggest all it wants. Holding one entity liable for the actions of an entirely different entity beyond the control of the former's is asinine, and I can guarantee you these automakers will gladly sic their armies of lawyers at a Supreme-Court-bound case and/or their armies of lobbyists at legislatively castrating the EPA if the EPA made any such attempt.
On top of that, the EPA is virtually irrelevant for EVs, and yet EVs are just as locked down (if not moreso), so I don't buy the "EPA might punish us" argument for that reason, too.
Why people want to trade off power for a big cloud of black smoke is beyond me, but there we are. If they want to get 50bhp from a nine litre engine, that's their concern.