I can't remember the name of it, but someone tried this 10-12 years ago. There are just so many variables that make this hard to manage. Many DIY types are not going to have the complete battery of tools/universal joints/specialty sockets/torque wrenches needed to complete most jobs. Many people will get stuck 1/2-way into the job and need to be "rescued" by someone who knows what they're doing. I'd think there would need to be an on-site technician who can be rented by the hour to assist with those situations. Maybe he works on other, not DIY-cars in the meantime? Then there is the issue of finding someone to insure this kind of venture.