Just guessing but I think it will probably work similar to how Tesla staggers software updates across the fleet now. Tesla will release a version of FSD to a portion of the fleet, see what the disengagement rate it, make changes, release a new version, rinse and repeat eventually, they accumulate say 1 billion miles of autonomous driving on the same version and the disengagement rate hits the right number and then Tesla can say that their FSD is good enough to remove driver supervision.
I'm talking about after it goes unsupervised. How does anyone handle new releases without reintroducing monitoring/ disengagements?