So while I agree with you, unless it were federally mandated for all cars, the ones that didn't do it would have lower cost of ownership and get more buyers.

Cars go back for recalls all the time. Having to physically replace a part isn't a big deal. Dealers have a supply chain in place for obtaining parts from the manufacturer.

Unfortunately, at least for some cars, all these options are bundled together in packages. Unless you buy the base model, you'll get the Internet as part of a package of other features that you want.

I think that nowadays the better answer would be to go in and physically rip out the cellular antenna. Easier said than done.

But instead of giving this chip which should be read-only regulated by software direct access to the bus, route it through a bit of extra on board circuitry which physically prevents it from writing data to the bus. This would enforce the readonly client in hardware, not firmware.