Comment by Nomentatus

My thinking is similar. Removing ultrasound may in the end be more of a legal decision than a purely technical one. I suspect neither humans nor ultrasound can deliver real safety under fog conditions or blizzard conditions; so it may be best to clearly fold under truly difficult conditions and cut lawsuits vs Tesla for fog crashes off at the pass. If drivers want to drive in fog; they will be entirely responsible for the results and can hardly argue otherwise.

This leaves the question of moving to radar, but for precise resolution well ahead of the vehicle you need microwaves and a lot of power, I would guess - which reduces the vehicle's range. For all I know you might parboil passersby, too. One old Mig had a radar that would kill and roast rabbits on the runway as it took off, but that's a much different use case, of course.