"Others believe that “enshrining” today’s already congested 1030/1090-MHz transponder frequencies into the legislation would further delay the urgent need for a better and more secure surveillance datalink."
Therein lies one of the biggest issues, the congestion which leads to drop-offs, the second major issue is the security and integrity of the broadcast. This is the major reason that Boeing does not support ADSB-IN systems, the lack of security in the broadcast.
In the US, the FAA is going to use 980 below 18,000 adding complexity.
The FAA mandate is for ADSB version2, unfortunately, Australia and Europe jumped in too early with mandating Version 0.
Given that the parameters are being argued, especially security/intergrity parameters of the ADSB broadcast, it is very likely that the Version 2 will not be compatible with version 0, but who knows.
This dialog on ADSB about sums it up:
But where is the pushback for technological change coming from?
Pushback: After working for the FAA for 31 years, I can tell you politics, politics, politics. The only tech advances that get anywhere are those that come from the appointed political management people that can use it to enhance their personal résumé and bragging rights. Suggestions from controllers, pilots, technicians, and engineers are almost always buried in beurocracy for fear of actually making sense.