I'm assuming Level 4 is what Musk means by Full Self Driving. The bar to be passed is then
"No driver attention is ever required for safety (...) self-driving is only supported in limited circumstances (e.g. geofencing), and when these circumstances are no longer met the vehicle must be able to safely abort the trip, e.g. park the car, if the driver does not retake control."
How would that work if you're out driving on the highway, and it starts snowing hard so the car can't see anything? Just park on the highway?
If your car can't safely handle such a scenario, the automous feature would have to be "season-fenced" in addition to geofenced.