I just don't see this being a problem. People don't go out and secure financing for a car or cut a $40k+ check for a weekend joy ride.
For regular, everyday people, sure. But there are A LOT of people with too much money that wouldn't blink an eye at dropping $40k for a free 1000 mile/7 day test drive, just for the lulz.. Rich folks are the cheapest people around, and if they can get something for free, they will.
I don’t think you understand how many unique parts each of these vehicles has. It is an impossibility (financially) to outfit enough mobile technicians with enough parts to service all vehicles currently on the road.
They would need part supplies, which they do not have, inventory hubs, which they do not have, a large fleet of skilled employees, which they don’t have, etc...
Who said anything about servicing all vehicles on the road? Who said anything about taking every single part on a mobile repair call? Hyperbole much?
The service centers do have the parts supplies already. They have the technicians already. If they didn't have either of those, they couldn't repair the cars at the service centers. They load up the parts and the techs in a car and go mobile. It's a good strategy that will work and save time and money.
If you call in for service, they can quickly identify the problem and necessary parts, and if it's something they can fix remotely, and they have the parts in the service center, they'll send out mobile repair with just those parts. That will probably take care of 50% to 75% of the problems people bring their car in for service. Door handles, latches, windows, MCUs, on-board chargers, trim parts, 12v batteries, and almost any electronic component can be brought along.
The other 25% they'll just tell you to bring the car in for service. We've seen the demo mobile repair cars at Milford fully outfitted with tools and parts, and it's really amazing what they can fit in there.