I have very limited knowledge of how car registration in the US works, but AFAIK some states, particularly California, have stricter emission limits. Does every car sold anywhere in the US meet them, or do manufacturers make cheaper "non-Cali" models that lack some emission controls but can't be registered in California?

Even if there is no regulatory hurdle, there's a significant practical one, which is getting the car over.

Even with the different emission standards, you're allowed to own the vehicle. However, if it does not pass inspection (if the state has inspections) then it won't be legal to drive as it didn't pass inspection. However, you're still allowed to own the car.

(Also, I wish I hadn't been down voted without a response. If I'm wrong, correct me.)

The digital goods sellers are going to have a field day if these laws end up allowing "Sure you can 'own' the game, but you can't 'play' it".