Agreed, which is why California would apply them to all cars sold in CA or brought into the state.

Essentially, they would just be an extension of existing state vehicle registration fees.

The test for violation of the interstate commerce clause doesn't care about intent. So, quite interestingly, if car manufacturers hadn't decided to only target CA emissions standards they would have been able to bring suit against CA if creating two models of everything was too difficult.

Would the solution of only creating one model and selling that have been a valid reason for a federal court to dismiss such a suit? I think it unlikely, as that would give CA de facto control over a huge amount of economic activity outside of its borders.