At this week's Drones and Aerial Robotics conference, Joseph Hall gave a presentation that discussed some of the issues around the idea of drones needing a "license plate" (and presumably drone operators needing a "drivers license).
His slides are now available here.
Also, here's an NBC article on the same topic, also taken from the conference. Excerpt:
One way to assure a minimum level of competence could be pre-use certification, a "driver license" of sorts for pilots who fly the birds.
Operators of small military drones like Ravens are trained before they can use them, and Capt. Adam Gorrell — who trained drone pilots and flew them himself in the U.S. Air Force, before becoming a professor at the Air Force Academy — sees a similar training system working for domestic operators, too. A different, smaller craft perhaps wouldn't need the same amount of training time, but the "mark in the sand" for flight readiness could shifted accordingly, he said.