The WAAS ADSB-out specification enables air carriers on adjacent taxiways assurance that they will not cross wingtips -- and even identify where an a/c ahead has held a bit too short to taxi past. It might have helped in Dublin where a winglet got tucked into an elevator
To conform to this spec requires a WAAS certified GPS source and a certified installation -- both very expensive for a GA owner
Allowing GA owners to bypass this gold plated certification rigamarole would enable air carriers to know when a GA aircraft in the air is a threat.
The fully gold plated ADSB-out is being forceably mandated in the US effective January 1, 2020, but GA uptake is low and the capacity of avionics shops to get this done for the entirety of the GA fleet is doubtful
