Taking this topic further, many times, perhaps the fully trained and aware autoPilot users that may become overconfident of AP abilities (yeh! I know how it works...) after 1000s of successful AP driving miles that they might momentarily lapse in their concentration - and if luck would have it, tragedy might strike. How to keep up with the overconfident drivers? Does Tesla need to? No - because there is enough legal clauses everywhere to protect them. But then, lives should matter more than a few dollars lost in market value.
Perhaps the car builds an AP reward system (that resets with every Drive->Park transition) to monitor driver attentiveness. Yes, driver-facing cameras are now in M3 (no s/w yet), but 100s of thousands of S & X don't have them. The logic could be: when the "hold steering wheel" message appears, a counter starts. If driver doesn't respond to that message in say 5 (or some other #) seconds, car gives a low point to the driver. After a few successive such slow scores, car can decide to turn off autopilot (or auto-steer) until the car has been put back to Park (after a stop). Basically, reward attentive drivers with AP, and take it away from those that are not facing road/screen (& missing the warnings). The car can build on this system and decide if a driver has never missed the 5-second warning, stop this reward system altogether, and those that get low-scores often, should be somehow notified/trained.
That brings up another thought, how can M3 driver-facing camera monitor face/eye movements at night/darkness? Wish they had apple's face-ID camera/IR system? Is Apple going to buy Tesla? hhmmm. another topic for another day.