Yes, the work at Google, NASA, and the FAA comes to mind. They are very aware of the need for handling this for the delivery space. With drones, as you pointed out, the flight path "conflicts" are much smaller. There are no wingtip vortices, and the drones take up much smaller physical space. The flights also start and stop much more rapidly. Right now, my impression is that the FAA is not equipped to process a major increase in flight path data with different flight conflict characteristics. Especially when the flight's round trips include a takeoff and landing. There are no "air corridors" in drone delivery, since below 400 feet, many more obstacles go into a flight path, and every house becomes its own airport.

As for drone GPS, there are VERY high accuracy options available using RTK. Especially RTK over satellite with systems from Trimble and Leica coming to mind. These are typically used in terrestrial survey and allow very high degrees of confidence in the physical location of the drones. I don't believe RTK works for planes, but it is in commercial use in drones all over. s

I don't think you need centralized ATC for drones, you just make it a swarm/network function. Drones don't need 1000 feet of clearance; they're smaller, lighter, slower, fly lower, and have high maneuverability. Even when we get to the inevitable air scooter stage for peoples I think a 50 foot clearance will be sufficient.