Francis, that is an easy one. I lived under the belief that WAAS was essential to the implimentation of ADS-B here in Oz...how wrong I was. ALL that is required is the FDE part of WAAS capable GPS, the TSO145a/146a versions. (There are avenues open to other specced GPS, provided they can demonstrate the same or similar integrity..if I am still correct in that regard)
Whilst WAAS would be simply fantastic to provide for CAT1 approaches to ANY aerodrome in Australia it is not required to impliment ADS-B. Upper airspace ADS-B is already "live". What happens next is anyones guess until the final NPRM comes out showing how the CASA and AirServices are going to direct their attention...my guess is voluntary fitment until critical mass and then mandate and restrictions to airspace for those not equipped to force as close as possible to 100% as per the original docmented proposals.
Since this argument started, the costs and availability of GA level equipment has "met the market" The cost to the feds is going to be minimal for the next bit...the cost is going to be "burdened", if you wish, on the owners. Luckily, it is going to be nowhere near what Leadsled T28(and his other guises) and Smith and another identity from your way, predicted.
My personal wish was for something like the US UAT receivers AND WAAS. Pipe dreams, I am afraid. However, my studies of how the Transport Departemnt in Japan put their capabilities into the MTSAT...there is still a real possibility of WAAS capability becoming available in Australia...the question returns to the bean counters and "User Pays" who the user is is the question...present Australian bureaucracy cannot understand common good as does the US DoD...the owners of said system.