I've never understood why Richmond doesn't get a run as a potential civil site. Has a distinct advantage of actually having an airport there to start with.....
RAAF Richmond has a 7000' East/West runway with the City of Richmond at one end and the City of Windsor at the other end - extremely noise sensitive and unable to extend the runway to make it suitable for medium/long haul operations. Also, it has a lot more fog issues than Mascot - not a suitable location for another Civil airport.
Also, the RAAF has had a gutful of the demands being placed on it by airlines (Jetstar, etc) since they opened RAAF Williamstown to joint military/civil operations. It is impacting on the RAAF's operations and they would like to go back to a purely military operation. There's no way that they will open up another RAAF base to joint ops. If there is a need/demand for additional civil airfields, it's up to the civil operations to fund the infrastructure - not rely on the military to provide it for them.