Cars are huge machines bound to roadways. Despite this people are constantly driving on suspended licenses, without licenses, without insurance, under the influence, speeding, etc. Regulating them mostly works because they're limited to specific spaces, are a huge time and money investment to construct, and so large they're fairly easy to monitor.
I don't see why the apparent "success" of license plates on cars means something even more convoluted will work for drones, which come in drastically different sizes, and are extremely simple to assemble and use.
We seem to recognize that licensing bicycles isn't really a feasible thing, and licensing tiny objects that move quickly in 3-D space, and which present even less challenge to assemble than a bicycle, doesn't seem all that likely to succeed with actors who want to do things outside the system. Or even cover people who just do stuff without thinking about it.
As technology gets advanced maybe there will be more of a carrot - maybe registration gets you access to autonomous navigational beacons and traffic control or something, and you'd prefer to have those things. But operating what amounts to a large cell phone attached to some electric motors unregistered seems like it'll always remain trivial for anyone who doesn't want to cooperate in a way that's not really the case for cars.
