"I understand the military has about 300 “ICAO” rated controllers, and once these people move over to Airservices Australia, there will obviously be plenty of controllers available."
Frank you understand wrong. Both on ICAO and numbers.
You are correct in that there are savings to be made in using the same system. Getting the military onboard is the problem. Have a look at Project Genesis.
It will take quite a bit of persuasion to get the military to give up airspace or become more flexible with it. We can but try.
Green Goblin, the military use a different system (ADATS) at military bases i.e Amberley, Williamtown,etc.