You'd be talking custom made machines, because you just know some idiot is going to hook a box of chow mien noodles onto the skid of a robocopter and it'll get dive-bombed by a pigeon and land on someone's wind shield in the middle of rush hour traffic.
The problem that robotic helicopters, and other flying devices, are going to face is that they're legally liable for anything they damage below them if something falls. When you're 50' up, you don't want to be dropping a single thing over a roadway or side walk. It also brings up the questions of insurance, registration (to ensure all UAV's flying are insured and maintained) and more, because any accidents have the potential to be equal to a motor vehicle accident in terms of personal injury claim.
Operators literally have to have no choice to make sure there's the ability for them to get sued for accidents/drops, otherwise municipalities will quickly outlaw them and once that happens it's going to be decades before those municipalities change their minds.
so what? there are thousands of car accidents and deaths every year that doesnt stop majority from riding. What OP did is open my eyes on something I didnt think of before. Imagine a crowded city, like NY where 5 feet above your head there are hundreds of drones like bees flying everywhere and delivering goods: food, small mail, lighweight groceries, etc. That would be great win for problems with traffic in big cities. Mother Earth would appreciate that too. Awesome idea OP.
EDIT: you could also have personal delivery done this way, something like "electronic mail pigeon". You attach your lighweight package and you send it across the city. Of course we would need to minimum probability of accidents. Most likely software used would have to be governmet-approved/tested and you would have to have a license to be a part of "lightweight transportation channel" that flows above the city. But this is totally doable!
Excellent visualization. You've nailed the kind of socio-infrastructural change this shift could lead to.
Licensure, state registration, federally-mandated commercial drone manufacturing standards, and liability insurance may sound like a damper on the future, but by ensuring a baseline of safety and reliability, it will ultimately open up the market to all sorts of innovation.