There's probably a non-trivial amount of model specific knowledge needed to repair a Tesla that can't be picked up at a general mechanics' school. Maybe when Tesla's sales volume increases there will be a higher demand for mechanics that Tesla couldn't fill and 3rd party shops will open.
disclaimer, I work a major auto parts supplier, etc. It will be very very interesting to see if tries to circumvent this law, which I doubt he can. If anything shuts down his expansion it may be through this route. As in, they may force them to curtail selling until they can provide the independent support.
Wouldn't that just be the same manuals, training videos, and parts-ordering-system credentials that they give to their own mechanics?
And the whole thing takes a turn for the absurd when you consider electric cars. Sure, force manufacturers to provide documentation on how to replace a bumper.. but its purely naive to think you could have just any mechanic service a completely computer controlled high-voltage battery compartment.