Comment by krisoft
> And then how do I loan it to a friend without the rigamarole of adding them as an authenticated user?
By making adding an authenticated driver not a rigamarole, but easy and intuitive.
> What if I'm not able to add them as an authenticated user or authentic myself to let them drive, e.g. I'm injured or very drunk?
They call you an ambulance.
In the future?
They call 911, and they read the license plate number and the authorities send an override signal that turns on the car and only allows it to be driven to the nearest hospital that appears on the screen on the console. If they go off course, they have 30 seconds to get back on course before it coasts into a 5mph limp mode (to find a safe place to pull over) for 1 minute before it completely stops and shutsdown and locks them inside for the police to come get them.
Eh, the car will probably be self-driving at that point, so probably only the first half.