FSD when it starts working, (there is no if IMHO), will be a pretty significant but minor milestone in comparison.
Most people aren't particularly good drivers. Indeed the vast majority of lethal accidents (the statistics are quite brutal for this) are caused by people driving poorly and could be close to 100% preventable with a properly engineered FSD system.
Something that drives better on average than a human driver is not that ambitious of a goal, honestly. That's why you can already book self driving taxis in a small but growing number of places in the US and China (which isn't waiting for the US to figure this out) and probably soon a few other places. Scaling that up takes time. Most of the remaining issues are increasingly of a legislative nature.
Safety is important of course. Stopping humans from killing each other using cars will be a major improvement over the status quo. It's one of the major causes of death in many countries. Insurers will drive the transition once they figure out they can charge people more if they still choose to drive themselves. That's not going to take 20 years. Once there is a choice, the liability law suits over human caused traffic deaths are not going to be pretty.