The AMA filed suit against the FAA, which likely prompted an FAA retaliatory action. People in power cannot tolerate being challenged at any level, and a lawsuit against the FAA by a non profit organization just might expose a level of ineptitude that will be even less favorably tolerated.
For ADS-B to work ALL aircarft would have to be so equipped. Under current regulations a great many civil aircraft are exempt from such equipment standards. All they have to do is be lacking an electrical system or avoid controlled airspace where such equipment is required. They are exempt from having any type of transponder or two way communications as well. See and avoid is a purely visual activity with that group and the success rate is less than 100%, even IN controlled airspace.
As far as the FAA and regulating what we do is concerned, I can only see their possible right to control in two areas. One is in flying for hire, which is pretty well defined in the FAR's. The next is the distinction between a model aircraft, which may now be moot, and regular aircraft. A multirotor is not a scale model of anything but a multirotor and each one is essentially "full" scale. And as a rule they are "unmanned". That latter definition is something that happened to me when I got married, but that's another story completely unrelated to aviation... In any case, by flying an unmanned aircraft that is not truly a "model" aircraft, for hire, there could be some legal wrangling that could cause people some angst. However, to date the courts have ruled against the FAA but their voiding the model aircraft rules might have significant impact on future rulings in this regard. The game is on.
BTW, very small Mode C transponders are already in existence and commercial use. They could still be a little smaller. I was in conversation with one of the manufacturer's on that subject yesterday. If the power output requirements were a little less they could become quite small.
