Even if this ever becomes a reality... which i am not sure it will any time soon... it will quickly stop due to a few aviation and non aviation related issues:
1. the manpower required to setup/prepare the drone for flight being such that it will far outweigh putting a load in a van
2. The number of drones that will go missing due to theft (either by overriding the drone, or shooting it down)
3. The cost of maintenance, and recharging the drones far outweighing the cost of the man in a van
4. The fact that depending on winds, there will be a number of days where they could not operate.
5. Depending on wetness of weather there will again be a number of days when they could not operate.
6. The fact that especially in a city environment, whilst carrying large-ish cargo the wind gust blowing down one street may upset the drone beyond recovery even though the forecast and winds were within limits.
7. The limitations of load being a major issue
8. The cost-benefit analysis outlining why it is a terrible business idea to do it. The cost far outweighs the benefit of the slightly faster delivery time.
9. You have to have someone on the other side who knows how to handle the drone, and how to detach the package, how to sign for it, how to tell it that it went to the wrong place, or that the person they need is not there....
The bottleneck at present really is the preparation of the packages for delivery, the delivery is pretty efficient as it stands! That bottleneck won't disappear with drones doing the delivery it'll just shift the bottleneck to the preparing the drones rather than preparing for dispatch as it will just be that much slower!
The only major enhancement they should do is actually give you say a 30minute slot when they will be delivering your package, and you be able to track the package / tell them you're not in, or other important information such as where to leave it!
A friend worked on the Domino's Pizza drone delivery advert. And although it was "just a stunt for
PR" - they also noticed that the pizza was completely cold even if it was straight out of the oven before being attached.
Anyway... that's my 2c!!