I've got to think that Amazon could rent out the roofs on commercial buildings throughout cities pretty cheaply. Doing so could completely moot the range issue as it would enable drone relays. I'm sure there will be regulatory barriers to doing that, but if they can get FAA approval for their delivery program as a whole, I'm sure they can get to a tipping point of municipalities that enable this sort of relay system. It might even be a Google Fiber sort of thing, where people actively lobby their municipalities to remove regulatory barriers so as to bring the city's technological capabilities in line with the state of the art.