And yet almost all car companies are—with rare exceptions—entirely averse to the modification of car software updates for anything more substantial than bugfixes, device compatibility and trivial tweaks.

It might not be a tech challenge, but it is a corporate one. It seems like no car companies want their cars to ever change in any way, lest a single word of their owner's manuals might need to be rewritten.

BMW for example will provide software updates to their iDrive head units: either as a trivial patch for device compatibility, or as a more substantial update applied by the dealer. And the latter sounds great... EXCEPT that their system configuration is guided by the car's build date, and if a useful feature was released after your car was built, you probably won't get it.

By way of example, my May 2013 build date BMW F20 shipped with no screen overlay for volume changes. In order to get that overlay, I first had to get the software flashed by the dealer (there was an actual crashing bug which was another story) and then I had to "code" the car myself to make iDrive think its build date was a year later. Once I did that, I got a screen overlay for volume changes.