This is my opinion, so it's coming from me and my realistic expectations of how legislation works in the US. The companies that have permits to operate autonomous vehicles have received those permits effectively after paying off lawmakers and states/counties/municipalities. A perfect example of this was Uber testing in AZ before running down the pedestrian crossing the road.
So, in my opinion, this is going to go one of two ways. States will pass 50 basic sets of legislation, and counties within them may add their own. This could range from all out ban, to specifying liability, to allowing what they believe will be the utopian future of machines driving themselves in public areas. We don't know, because there aren't any good models yet. Alternatively, the federal government could get involved because of the extremely high likelihood of these vehicles crossing state lines with and without an operator inside them. If that happens, I expect it will take even longer, because each state will take on its own rules. This is pretty much how things work now in real life, so I see no reason to not expect the same.
The most likely outcome of all of this is that we live in a very small bubble where we think robot cars operating on their own is a great idea in most cases, but the public at large does not and will fight any attempt to make autonomous vehicles a normal thing until they themselves own one. This is again based on my realistic view of how society works here in the US, and loosely how it works elsewhere. This isn't FUD, it's my educated guess. So maybe it's UD? Because I'm uncertain that FSD will be allowed nationally within the next 18 months, and I doubt legislation is actively being worked on now on a national or wider state level.
BTW, CA does not represent the rest of the US. This should be very clear to most people by this point, right? And most US citizens live outside CA rather than inside.