abgd, it sounds like you're involved in the R&D / development of the project. It is a cool project to work on, and I would suggest keeping at it whilst Amazon keeps paying you money - but I simply don't see it (EVER) becoming a reality.
Not trying to crush anyone's dreams... But there are too many legal issues that will arise, too many "what if scenarios". If the school cafeteria cook gets laid off or helping a kid who climbed a tree and couldn't get down, by bringing a ladder... How on earth will Elf n Safety allow 30+Kgs flying over very busy roads, with thousands of people, vehicles, houses, offices, properties, emergency helicopters flying low, police helicopters flying low....etc...
The question is not "IF" they crash, it is "WHEN" they crash. THEN what - who goes to jail, who pays for damages, who compensates families who lost loved ones, who cleans up the mess on the streets / roofs / river / ponds / other....
That is why it won't happen!