Amazon has just gotten a patent for an "airborne fulfillment center utilizing unmanned aerial vehicles for item delivery." Though the patent was granted in April 2016, the plans for it have just gone public on the US Patent and Trade Office website. What they describe sounds like something out of a Philip K. Dick novel.
Here's how it works. First, get a very large airship and float it above a city. Then attach a giant warehouse full of Amazon items to the bottom (actually, you should probably attach this before the floating, but the patent is vague on this point). This warehouse is constantly restocked by smaller airships, which bring personnel and supplies from the ground, as well as carrying away waste. People on the ground use their computers to browse items currently floating over their heads, and order whatever they want. Then drones grab the items, hurl themselves out of the airship, and engage their rotors as they approach the ground. The human receives his or her item from the drone, and the drone ascends back up to its floating palace of boxes and workers.