I think access to source code is a key enabler. Even if it was limited in some ways, that would be a good start.
Imagine if Consumer Reports could access the code and do a code review when testing a car. We know from lawsuits that Toyota software is absolutely horrible, for instance. I'd think that insurance companies and consumers would benefit from knowing that up front.
Or imagine if repair shops could get certified for access to the software to modify it. Mod shops already do this on the sly--they're just hoping to fly under the law. Maybe they have to carry a bond, like home contractors.
On an Android device or Chromebook there is a user-adjustable setting that permits root powers. If there was a liability standard about this capability, then maybe more companies would feel comfortable offering it.
The ideal would be full source access to everything, but I think there probably will have to be some intermediate steps or limits, as a means of compromise.