They'd have one group of programmers developing the core products, but then another (maybe much larger) group of programmers who are the tech assets on teams standing up partnerships with dealers. Since most dealers are independent businesses, there's probably a wide diversity of software stacks and levels of tech competence.
Personally, I wouldn't buy a new automobile until everyone has open access to these propriatiary automotive computer systems? I think that date is around 2018? If interested read this blog:
https://ifixit.org/blog/6305/you-gotta-fight-for-your-right-...
But then again, maybe no one cares? I know Saturn engineers tried to make a repair friendly car(you could get to failed components, but no one seemed to care?) This was before the Internet though? Times must have changed?