This is neat, but unfortunately ADS-B will not be required for all aircraft in 2020. It will only be required for aircraft within a 30 NM circle of certain major airports and inside (and above) class B or class C airspace.
Realistically, most will probably install ADS-B out transponders. But there will be areas where pilots fly (Alaska, Pacific Southwest desert areas) where it won't be uncommon for airplanes to be missing ADS-B out.
I think this is great and will encourage the industry to do the same to compete. Of course, not aircraft will have this and it doesn't replace maintaining LOS but more situational awareness the better. Eventually UAVs and manned aircraft need to share the same immediate airspace and this is a step in that direction.
Realistically, most will probably install ADS-B out transponders. But there will be areas where pilots fly (Alaska, Pacific Southwest desert areas) where it won't be uncommon for airplanes to be missing ADS-B out.