I thought this thread needed more input, so...
I always add 50% to any estimate of time or money, so three years could be closer to five. A lot can happen in that time.
I work for the world's largest retailer. Our executives dismissed Amazon's drone delivery commercial aired X number of years ago, as a publicity stunt. We have tried drones in distribution centers, to take inventory, and spot check product facing, but like all things tech, the conditions have to be perfect. It is much easier to accomplish the same objective with scanning machines on wheels, even at DC stock heights. Even then, tech only makes financial sense where labor is tight. While solving the dilemma of 'the last mile' is cause for salivation, not all drone deliveries will be within a mile of the DC.
Still, what happens if the commercial drone industry 'floods' the sky with 'same day delivery'. All that constant buzzing as they descend. Will people select that delivery mode, or socially/collectively reject it?
The commercial industry presupposes people will tolerate drone delivery. I find that hard to believe. Will people down the drones? If so, the lost products will add up to the point that drone delivery is not worth it to retailers. Not any of the tests have been to commercial scale, yet. To my recollection, real world tests have been the occasional drop off, and for medical supplies. Rarely does financial modeling play out as designed. The ROI may not be real.
Regarding a safe airspace, while drones out number manned aircraft, how many are up in the air at any one point in time? I'm sure the numbers are greater in densely populated areas, but not so much in rural areas. I've been flying for three years, and I've only seen another drone twice. Do we really need a blanket policy, or a more demographically tailored policy?
Regarding the bad guy, I'm sure the bad guy effort will be recorded somehow, but stopped? If I remember correctly, the only thing that prevented the assassination attempt in Venezuela (?) was a drone technological failure.
Regarding enforcement, unless there's a new drone task force, I don't see existing police forces stopping everything to pursuit a senior citizen drone pilot. Maybe the FAA or other would issue you an auto generated ticket like the cameras at intersections can. And, if you fail to pay?
Regarding privacy, just as Amazon works with the USPS, the US(PS) could work out a deal to install surveillance equipment on commercial drones, or be suspected of doing so.
In the spirit of cooperation, would it not be possible to elevate the floor of manned aircraft from 500' to 650, and have the commercial drones fly from 450 to 600'? The commercial drones will be more powerful, and computer controlled, so the more narrow space should be easy to navigate. Also, commercial drones would likely start from distribution centers, even pizza. The DCs would be on the outskirts of town, fly straight up to altitude, and then, within their assigned altitude, across to destination, before their intolerably noisy final descent.
I suppose a floor of 550' for manned aircraft would extend the airport radius forbidden zone, but not that much. Geometry anyone?