There are already draft regulations in California [1] for exactly this. I expect that at least some states will have cleared the way by 2018, though obviously not all. Autonomous driving will likely be location-restricted to start with as a result. Remember, there is a lot of pressure on politicians from many companies and people to get autonomous vehicles on the road as soon as possible.

[1] https://www.dmv.ca.gov/portal/dmv/detail/vr/autonomous/auto

NHTSA is scrambling to make it possible, this is the biggest safety innovation in cars since the seat belt. And as long as they have the hardware capabilities, Tesla wouldn't have to launch it with full autonomous mode available.

Just imagine how safe we will be if we reach Level 5 autonomy, no driver control possible? I think the Model 3 is going to be the first production car to reach Level 4. I'm hoping that's what the "part 2" update is.