The “what and where” requirements are easy to enforce. If a drone goes out of control and strikes a person, it was clearly in violation of a rule against flying over people.

“Return home” is a good start, but it is not enough. The feature set also has to include “see and avoid”. If it can decide to “return home” directly into the side of a manned balloon, it is not safe enough for unrestricted autonomous operation.

I say this as a balloon pilot who has observed drone pilots operating in the vicinity, and even attempting to land on top of a manned balloon.