How about a mechanical fail-chute? The UAV could be equipped with a dead-man switch style parachute/inflatable life raft contraption that would trigger if the rotors stopped turning and if the device was flying high enough, it could float harmlessly to earth cocooned in a pocket of sturdy material buffered by some quantity of air. If you could figure out how to make it work, you could be in about as much danger as getting hit in the head by a beach ball...
Yeah, that sounds like a good idea. It's probably not going to be implemented across the board without some level of regulation, though. If they get to the point where they're passively safe, and require little skill to operate safely, the govt. might get to the point of fairly relaxed restrictions on them, like drivers licenses now.
