Bumping this a bit since I'm doing drone research, but am a fixed wing airplane pilot and have installed and owned multiple ADS-B transponders in manned aircraft.
CAVEATS
- ADS-B uses two frequencies, 978mhz below 18,000 and 1090 mhz above. The only way to get a 'complete' traffic picture is to get 978mhz from a ground station, which is sketchy at the moment due to ADS-B config on the FAA's end (you must be broadcasting to receive, otherwise the towers 'sleep' if there are no ADS-B transponders in their sector
- You will only get ADS-B equipped aircraft on 1090 mhz without a ground relay signal, and that is not all of them by any means. As you mentioned above, the deadline to equip is not until 2020.
- The reason that it isn't picking up military traffic is because the military has not equipped anything with ADS-B in all likelihood. They are bad about refusing to play by the FAA's rules, they did the same thing on RVSM altimeters for flying at jet altitudes (they simply refused to equip it and flew them lower).
ADS-B is great in an airplane for traffic, but no airplane should be flying below 500 feet away from an airport except in case of an emergency (with the exception of things like J3 Cubs puttering around without any sort of electronics in them at all). In short, if you are flying your drone in class G airspace as you're supposed to, you're going to be hard pressed to find an airplane to run into if you are legally far enough away from an airport to be flying the drone. If you do find one, it should be bright yellow, slow, and easy to see (google a J3 Cub

).
All of this of course does not account for helicopters, those are the bigger threat to drones in my opinion and vice versa. But ADS-B isn't going to protect you from hitting one without some form of TCAS, which is a whole other layer of complexity. (TCAS is an on-board radar that finds traffic on its own, and won't let you hit it. If you get into a possible collision scenario TCAS seizes control of the airplane from the pilot via the autopilot and maneuvers to avoid the collision on its own. This is far away from drone technology for obvious reasons.)
If anyone else has any ADS-B or airplane traffic questions, feel free. I'll have lots of drone questions shortly.