I'd buy any Tesla, even the big truck, if it came with open source software! I don't want a car that's spyware like a phone. Let me be in control of it, let me mod it, let me own it.
Not exactly what you are asking for, but did you see that Rivian recently provided a way for owners to disable the vehicle's LTE connection? It's straight In Canada. In the US, you have to ask a dealer.
There are plenty of FOSS engine management projects around. There is a big community of people doing incredible mods. But cars are complicated and to do it well requires a lot of time, effort, knowledge, money. I've blown up plenty of engines along the way, and it's fun and I'm learning a lot, but it's not something that's easy to just dabble in.
See also this interesting slide deck about the GPLv3 and cars, I expect that regulations would mean you could not drive cars with modified software (similar to what happens with solar inverters):
Root persistence is more for encouraging you to report all bugs you’ve found instead of holding on to them in fear that the vendor will patch them and make further research difficult. See Apple’s security research device program.
The company that doesn't froth at the mouth for a constant revenue stream by selling every bit of data it can siphon from you with digital leashes. With most of business and startups focusing on short term high gains there's little incentive to build a real company that will think long term while actually giving a shit about its products AND customers. That all died out long ago. That kind of thinking is radical these days.