Leadsled, there is no airspace proposal for Western Sydney yet. There is an airspace concept in a document that dates back to the 80's. I suspect this is what you saw.
You need to read more on modern nav technologies. SBAS and GBAS are not GNSS approaches. Fleet equipage at the major RPT level is much lower than you think. Designing an airspace model on these capabilities would not be a smart idea.
Been designing for a long time, never heard of these "low noise" procedures you speak of. Are you perhaps referring to RNP-AR?
Still waiting for you to provide the ICAO airspace design concept you recommended we adopt in your previous post.