They'd lobby even harder to not have to meet CARB requirements. This is already playing out with the people in DC framing the issue as CA forcing their crazy climate beliefs on the other states and that is killing jobs and is wrong and must be stopped. If the tax credit goes away (which as you noted will disproportionately hurt the sales of compliance EVs), expect attacks on CARB to be intensified. CARB (and the dozen or so other states that follow CARB rules) is able to have stricter clean air standards than the Federal reqs b/c of a waiver granted under the Clean Air Act. So I'd expect that waiver to be the target. Bush attacked it years ago, and Obama reversed course. Whether they can succeed in the face of the inevitable lawsuits from CA (and most likely the other CARB states) if they try to do that is another question. But certainly the lower sales without the tax credit would play to the advantage of the Feds/Car companies, as they'd use it to show that the regulation is onerous and customers don't want their clean cars, and that they cannot sell them profitably, as the tech isn't "ready" yet. The counter argument is now we have Tesla, showing that you can make EVs that customers want (Tesla needs to become profitable to really drive this point home).
I think the CARB waiver under the CAA is most likely going to be attacked / weakened by the federal government, regardless of the ZEV credit status. Seems like they've attacked or dismantled so many environmental regulations already that they'd be unlikely to stop.
