I always assumed that drone delivery was just a publicity stunt (in urban areas anyway). I am hoping that it stays that way. I am really not convinced that a sky full of buzzing drones delivering people's toothpaste and takeaways is a great idea.
But it would probably makes economic sense. A big cost of delivery is the personal that actually does the delivery. It might not be viable for all packages but probably for the premium delivery that promises sub 1 hour delivery.
Only if you don't price in all the externalities: loss of delivery jobs, environmental cost of the drones, cost of drones hitting people, cars, buildings and powerlines etc.