FAA's NextGen is heading straight for a massive $40B failure. A big part of that problem is a severely distorted, misguided, ADS-B concept (far from the original ADS-B intent), that is now overspecified in key aspects (e.g., overspecified NIC and NAC), while failing in other critical areas... (all vehicles need to see each other directly, even UAVs - not via using ADS-R [ADS ridiculous] or UAT [Useless Aircraft Transponder]). ATC advocates claiming that ADS-B [in the US] needs WAAS level of accuracy and integrity are simply wrong. That's because FAA has NextGen's balance for C-N-S completely mis-designed and wrong, incorrectly assuming that ATS's future is based on and depends on essentially using PastGen's 1940s "pseudo radar" vector concept. FAA's ADS-B is simply not going to work, at any cost (which is still substantial, and well over $5K for any reasonable installation - don't believe one word of the commercial
PR blitz now being put out by the ADS "junk dealers" and avionics shops for $1999 units, that aren't installed, and aren't even anywhere on the path to future [real] ATS modernization needs).
Instead, FAA should scrap 91.225/91.227, allow for the airline delay of ADS equipage to at least 2025 (which FAA has all but already agreed), and focus on design of a proper NextGen, based on RNP based trajectory [state vector] exchanges [with any data link], and use of a redefined ADS-A, ADS-B, and ADS-C criteria, that are more relevant, practical, affordable, and not massively overspecified, as the present absurd TSO and RTCA specs written by the avionics manufacturers, largely to cater to seriously misstated FAA (false) requirements, while unnecessarily driving up avionics equipment complexity, cost, and ultimately profit.