Waymo has demonstrated solutions for many of the edge cases you mention. This video is from 3 years ago: https://youtu.be/tiwVMrTLUWg?t=530
Regarding snow, it maybe a difficult problem, but if cars can't see road markings, neither can humans, so how do they do it? Sometimes by following a car in front. Though far from real autonomy, my Tesla doesn't need to see road markings for autopilot to work, it will fall back to following the car in front.
And.. Why does Waymo have to solve this inclement weather problem now? Surely it would be better to demonstrate safety in good weather, then light rain, then heavy rain, then light snow? They can just refuse to operate in bad weather unless they are confident about it.