Airservices had a plan; it was called Ground-based Regional Augmentation System (GRAS). Basically SBAS but without the 'Satellite' - the GPS corrections being broadcast via VHF data transmitters. Bill Ely's thesis is a great overview of the history, and can be found by google search. Unfortunately despite substantial effort by individuals within AsA, that plan did not come to fruition.
The biggest drawback to SBAS for Australia has been the cost of the satellites to host the SBAS transmitters - but hey, guess what we're getting with the NBN...
NBN Satellites For Remotest towns 