Oz Bus Driver I can't see what a mode S transponder has to do with NEEDING ADSB !!!!!!!
Autralia simply DOES NOT NEED low level ADSB yes I fly in the U.S. and there I DON'T NEED ADSB.
I just crossed Australia in a 40 year old War Bird and I DIDN"T NEED ADSB, got to Perth no hassles and only used the VHF for CTAF entries, my trusty 406 EPIRB was with me, no need for any ATC services what so ever other than Bankstown GAAP to say goodbye, Parafield for transit and Jandakot to say hello.