This whole thing looks pretty overblown to me. It seems people are trying to take the concept of air traffic control at airports and applying it for potentially millions of devices in much larger free space. The main assumption being that air traffic control works great so lets "scale" it up. The thing is that air traffic control is centralized and comes with all the bad things associated centralized systems, bureaucracy, thick regulations and lack of efficiency not the least of it. Flights are routinely delayed, planes often circles around in air for no reason - all because of inefficient centralized traffic control model.

The alternative is the traffic control model we use on roads that actually scales up. Cars can go wherever they want and whenever they want as long as they don't enter prohibited areas, remain under certain velocity and don't collide with each other. I think this would be perfect model for drones. We can have two types of drones: (1) which are equipped with level of tech that can do obstacle avoidance and have restrictions map (2) all other. The category 2 should fly below certain altitude and weigh below certain limit. Category 1 should be able fly anywhere as allowed by restrictions map. There is no need for centralized air traffic control.