Getting mail 6 days a week is not necessary. And if this allows a knife to cut out all highway routes and some rural ones and replace with only drones that would be advancement. Mail is not a right but glued now to legislation. No need if nothing-above-me areas get only drone service.
I ponder this. As the ups and FedEx and Usps guys converge in the same address, we often talk shop. I wonder what an Amazon drone would say to a competitor drone when they are at/near the same address? "Man, my supervisor is always watching me?" or "they loaded up this flier unbalanced"