Make no mistake, drone delivery is not planned to be the way most amazon packages are delivered, ever. It's a high-cost "I need it now" service, that's it.
I'm not sure if that makes a lot of sense... how would they recover the drones? Drones have a pretty short range.
That's where the sharks come in.
If they can solve launching a drone from altitude from an aircraft without a rear cargo door at 250MPH without shredding it to pieces finding an efficient means of collecting them would be an easy task.