[fjtorres]

I have my doubts but they are regulatory in nature, not technology-wise.
Which is why I expect the ongoing Chinese tests will move faster than the Aussie campus-wide effort of Amazon's city-wide experiments.
The technology today may be limited to a kilometer or two radius but battery tech is improving regularly, with several bleeding edge technologies offering the promise of a tenfold energy density increase. Likewise, materials science and additive manufacturing can probably cut the weight of the frame a bit. I figure a 10-20 kilometer radius should be doable fairly soon.
Given the proper regulatory support, the traffic-choked cities like Manhattan, London, Tokyo, Rio, and the bigger Chinese cities would be naturals for high-value urgent deliveries, the kind of stuff that is typically messengered around. I could see computer components and software making a good portion of a potential Amazon 1 hour delivery system.
Economically, it could work as a corporate subscription service since most major major businesses have loading docks suitable for microcomputer drop-off.
Don't forget, Amazon isn't just for consumers: they do a lot of business in the corporate arena.
Don't discount it; the tech is being explored on three continents, so far, and that's because there is a place for them.