"NASA is working with industry and the FAA to create a new low-altitude air traffic control system specifically for drones. Industry and government officials say such a system will be needed if there are to eventually be widespread drone deliveries by Amazon and other companies [emphasis added]."
It's not a matter of "if," rather just "when." It'll be tough to control "some" of the sUAS at low altitude w/o controlling "all" of the sUAS at low altitude.