I'm a UK airline pilot. I can't comment (usefully) on the legal aspects of these devices.
With regards to the Amazon proposal: I think it is certainly something we'll see in the future. There are serious obstacles (no pun intended) to overcome before I can ever see it becoming reality.
In commercial aviation, safety is a priority, or at least it should be. How would Amazon deal with a failure of an in-flight drone on a delivery? Until they can safely land a drone with a technical problem, then I can't see it becoming reality. Bearing in mind that these are likely to be operating in built-up areas. The risks to people and property is high. The risk of collisions with other drones is relatively small and can be mitigated by good policies.
But when a drone goes through your greenhouse, conservatory or worse your precious Corsa,... Well.