Underfire, your comment "In the US, ADSB will not be required for at/below 3000 feet, because of the coverage issue." only tells some of this story.
In the US, any aircraft (IFR or VFR) operating within 30NM of an aerodrome with Class B airspace requires ADS-B, regardless of altitude. There are about 36 of these airports with Class B airspace - of course these are the busiest airports in the US.
Only telling some of the story is misleading and possibly damaging to any arguement being put to our regulator about being more pragmatic about ADS-B requirements now and into the future. I would encourage those with an interest in the US system to make sure they're well versed in it before making assertions. (
https://www.faa.gov/nextgen/equipads.../requirements/)
Of course Australia doesn't make use of Class B airspace - yet, although it is promulgated in AIP in the event it's needed. With Sydney's second airport coming on line early next decade I would suggest the SY airspace will become even more complex and therefore the need to incorporate this standard may be considered. And with ML and BN new runways coming online they may follow. This would result in EVERYONE within 30NM of these airports requiring transponders and ADS-B.