You can argue to NHTSA, sure. Good luck.
NHTSA forced Tesla to do a recall because the in-car computer allowed the owner to play custom audio on top of ("obscuring") the pedestrian warning tone.[0] If the in-car computer allowed them root access, NHTSA would have an aneurysm.
> as long as manufacturer doesn't provide a script or otherwise encourages you to `kill -9 safetyprocess` or something.
Doesn't matter.
Scripts will be circulating online within days. If Tesla doesn't stop it, now they're knowingly complicit. Headlines will feature sympathetic low-knowledge users who followed directions, reasoning that it's safe because "why would Tesla let me do it otherwise??" Fin.
--
A rooted car is a nice dream, but it's just a dream. We'll never be allowed to sell a (fully) rooted car, just like we can't sell a fully-rooted (w baseband) phone. The Wild West is over folks! Last round's on me... :)
If we're very lucky, some manufacturer might give root access to a (heavily firewalled / air-gapped) media computer.
[0] https://static.nhtsa.gov/odi/rcl/2022/RCONL-22V235-2686.pdf