I don't think this works? CA law already says cars registered to nonresident owners but used primarily on CA rows have to be registered in CA.
Scheiner specifically emphasized that the interstate registration system avoids requiring a vehicle to pay more than one full registration fee.
Why do you think they made this new law? It gets them to what they actually want, which is collecting tax.
Thats primary school level of math that in 2026 would be trivial yo implement, if fairness is the goal. We have such thing in Switzerland, you dont pay flat yearly fees/taxes/insurances if you register your car in december for example
Re: the pro-rate for a December registration, in California at least, registrations are renewed on the date you first registered, not based on the calendar year, so there's no need for a pro-ration.