Tom,
If I understand you correctly the augmentation systems you mention are basically the domain of the heavy passenger jet. What about your turbo prop and GA aircraft operating IFR into places other than where there is already an ILS or VOR? I don't think they can use stuff like DME/DME or other land based nav aids for augmentation even if they were available. These aircraft make up a significant proportion of the IFR fleet.
ICAO have a recommendation to have approaches with vertical guidance to each end of the IFR runways at all airports. Many Civil Aviation Authorities and ANSP's are adopting the ICAO recommendation. I know this includes the NZCAA and Airways NZ and likely CASA and Airservices.
While Baro VNAV fulfills the vertical guidance role for some aircraft it has some serious issues. For the majority of IFR, non jet transport aircraft, SBAS is the only game in town now and in the foreseeable future. No one I know of makes IFR certified avionics for these aircraft which has augmentation other than SBAS, nor are they likely to in the future. Like it or not all of this gear comes from the US and they have SBAS and don't need to cater for anything else.
SBAS gives approaches with vertical guidance to pretty well anywhere without the need for nearby ground based aids. To me it seems a perfect fit for Australia with its vast area and many remote airfields that would benefit from an IFR approach with vertical guidance. I'd imagine the likes of the RFDS guys and girls would appreciate such an approach on a dark night into some of the places they go.