I could rattle off countless problems with this just off the top of my head....
How are they going to prevent theft / tampering with the drones?
What energy source do the units run off of?
How will they travel long distances?
What happens when a drone fucks up an an order is lost?
Will each order be shipped out in a new one of those fancy ass hardshell plastic boxes?
...I'm calling bullshit on this one as of now.
It is a cool idea and I have no doubt this will be implemented in the future but as of now this is way too poorly thought out to become reality in the next few years.