Is it plausible they can use the large GPT model, to distill a smaller car driving model only from it and then run that onboard. Seems like that will solve all your issues.
Because having to offer upgrades to so many cars is expensive, Tesla puts a distilled model on older cars that performs worse and has no redundancy.
Time will tell if he can get away with this (hopefully not) but you are describing a system that's near-L4 and already exists today.