That's a non-starter in most countries. Since the car software is tied into a number of important safety features and regulated controls, custom operating systems will never be supported.
There are already massive problems with people miswiring head units to play videos while driving and updating their ECU to spew pollution into the air. You're not going to convince any significant number of people that it's a good idea to allow arbitrary code to run and control most of the other systems too.
The free-software and right-to-repair communities have a different weighing of tradeoffs than you do.
“Users shouldn’t be same to control their own engines actually” hmm well ok then
> Since the car software is tied into a number of important safety features and regulated controls, custom operating systems will never be supported.
Then that's a poor design that should go the way of the dodo. Someone hacking the entertainment system should not be able to take over control of the engine. The entertainment system on planes do not allow one to hack into the autopilot. There should be no need for a firewall, they should have no shared wires between them.