If California regulation de facto prohibits out-of-state cars from being sold or operating inside of it the rules may run afoul of the interstate commerce clause.

At least in the history book I used there is a direct parallel: a precedent setting case had to do with regulations about tractor trailer wheel mudflap sizes. States would set different conflicting values so that they could restrict the traffic through them (or force a waste of time before coming in).

There may also be another argument based on how states must, in general, respect each other's licenses (marriage, driver, etc; but interestingly not concealed carry, something I suspect will be tested again soon).