The Mode C veil is not going to go away. Instead, in 2020 you will have an additional requirement of either a Mode-S transponder with extended squitter and GPS position reporting encoded into the extended squitter (known as 1090-ES) to replace your Mode-C transponder, or you can have ADS-B Out (978 UAT) in addition to your Mode-C transponder. You get to pick your poison.
Note: this 2020 requirement only applies with few exceptions to the same areas where Mode-C is currently required if you have an electric system equipped aircraft. FWIW, I currently use a Mode-C transponder and ADS-B weather services (FIS-B) along with PCAS for traffic avoidance. By the end of this year, I plan to have my KR fully equipped with ADS-B traffic in (TIS-B in) and out (TIS-B out) along with ADS-B weather (FIS-B), all through my GPS with a 978 UAT to go along with my old Mode-C transponder. If you fly around traffic very much, you'll find these services to be quite handy. -Jeff Scott Los Alamos, NM