And insurance :).
Having 10-30kg high-speed flying machines, built by the lowest bidder and operated by companies that like to move fast and break things, being hurled around above densely populated areas full of squishy people and car traffic... how long do you think it will take before a first fatality? Do you want to live in constant fear of getting hit in the head by a low-flying brick?
No, a thick regulatory straitjacket is the only thing that can enable drone delivery in cities. But then, there's little point to even do that, until the noise issues are resolved.
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On a related (and likely just as improbable) note, perhaps cities should start treating delivery as another municipal utility. Right now, most houses and apartments in a typical city are fitted with pipes that bring in water, gas and fresh air, and take away sewage and stale air. I can envision another utility - a "package pipe" - a conceptual blend between old-school pneumatic tubes and parcel sorters. Imagine each apartment having an outlet sized for a standardized container[0], through which packages could be sent and received. I bet it could cover upwards of 90% of delivery needs of any town - most things people send would fit, larger orders could be split into multiple containers, and bulkier things would be delivered by trucks on-demand.
An installation like this would deliver all the benefits and solve all the problems of in-city drone delivery, cheaper, safer, better, and without any of the noise issues.
The obvious drawback would be the costs of building it up and maintaining it. Someone would need to do a calculation, but I suspect it could be paid for the same way other utilities are (small fixed payment for access + pay per use + whatever other bullshit business shenanigans electricity providers usually engage in). Looking at the cities I've been in, most existing buildings could be retrofitted with it as an external attachment (imagine an external lift going to every apartment). The big problem I envision is routing the inter-building segments of the pipeline - it would likely have to be above ground due to size, and thus expose it to the usual problem of landowners trying to extract as much money as they can from the public to let the project go through their plot.
But hey, one can dream :).
(My bigger dream is that one day, we'll all have something resembling a Star Trek matter replicator, perhaps in a form of sophisticated 3D printer fed from a municipal "matter stream" supply.)
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[0] - Say, UPS 10kg - "16.5in x 13.25in x 10.75in (42cm x 34cm x 27cm); weight limit 22lbs/10kg", or UPS 25kg - "19.75in x 17.75in x 13.25in (50cm x 45cm x 34cm); weight limit 55lbs/25kg". Via https://www.ups.com/us/en/shipping/create/package-type-help.....