Medium (small GA) sized drones, and "drone ports" aka numerous, smaller, autonomous-only, airports would probably be a much easier sell to the FAA than door-to-door drones. The traffic issues would be much easier, and they would also be a better fit with the current airspace.
You need this piece of the puzzle for door-to-door delivery anyway, why not do this instead of jumping right to the more controversial low altitude drones?