Chances are there is OSS already running in commercially available vehicles.
Owners tinkering with ICE vehicles was and is a thing and I don't see how an electric power train makes that too much different.
Open standards and data formats would be a good middle ground to help avoid the type of problem with Fisker "unable" to migrate to a different provider. Although I wish that vehicles did not have to phone home to the mother ship at all.
Just because the source code is open source doesn't mean the upstream repo going into your car has to be run by a toxic community with a chip on their shoulder.
"My car shuts off when I open all the doors"
"Why would you want it to run? You can't drive with your doors open! Marking as won't fix, working as intended."
"It's open source! You can fix the code yourself!"
No fucking thanks. Some things should cost money and have real stakes.