As someone who has worked on self driving for a few years, and holds some patents in the space - I do not feel at all qualified to make a guess. It is always a little odd to me, then, to see how many folks are. Can we all tone down the confidence? Skepticism is healthy, but armchair expert-ing is not.
Carmack is a genius, and 8 years is a long time. If we look at what cruise is doing in SF, it certainly does not seem impossible.