I'm afraid it will be the same as image recognition technology. It's "easy" to get good image recognition that works in 80-90% of the cases, but it still fails at the easiest edge cases(best image recognition in the world fails at telling a difference between a zebra and a sofa in a zebra print). So I think we will go through a few years of manufacturers making cars which can drive themselves in perfect weather, but we won't see a car that can drive in all conditions for at least a century.