Maybe in the future cars will asymptote towards the upper limit of mechanical efficiency (for each given class, like the school run, city trips, long distance, etc.), allowing users to keep them on timescales similar to homes, so the only profitable innovation will then be on the software. Then we might see "car-OS wars" and the beginnings of open source driving systems in parallel.

Nobody is stopping you to start those free open source "car-OS" right now. Considering this is actually embedded it's actually easier then writing a general purpose OS like Linux or Windows.