Don't get me wrong, i am all for the advancement of the tech in whatever fashion it manifests itself. Perfect example, the Segway.
The Wright brothers did not have to deal with congested areas and personal property damage. Back then, you could fly across the country and never fly over someone's home or major highway packed with carts. Get it? Carts instead of cars? Being time relevant. You are talking about putting a couple pounds of material over the heads of lots of people at heights that could kill someone if the battery died/malfunctioned, if you lost a motor/esc/fc, if you lost radio communications. Then their is mall intent. Some bent teen intentionally crashing into people for the kicks and no way to trace it back to an individual.
This is not even considering what a quad would do to a jet engine if it was ingested. Birds can take out an engine and they are soft hollow bones, flesh and feathers. Quads are carbon fiber with bits of metal attached. And again, the possibility of untraceable malfeasance.
Road rage? well, i will just cut off your legs with my quad bike. A pedestrian steps in front of a car and gets banged up. Step in front of a hover quad and you are missing body parts and bleeding out before help gets there.
Too much liability for the insignificant gain in quality of life. Electric cars will nix quad crafts. Now quad cruises, quad boats, now you are talking. Could go island hopping without worrying about the water conditions. God help the jet skier who gets too close.
Fascinating tech with practical applications. But i wouldn't go mortgaging your home to start a quad business. Right now, the Chinese own the market and will for the near future. The average shelf life of a new motor/fc/esc/firmwear is 30 to 60 days before it is old news and selling for the cost of shipping. No money means no big push for advancing the tech or applications in this country.
Liability will severely restrict potential development as well. For good reason.
it is a hobby. Enjoy it and don't go betting the farm on a big future the Chinese will gut you of profits for in less time than it took you to write the code.
Home built hover water craft. Think about it. Will suck to fish from though. Especially if you are trolling.