Avalon is for defense sales. The rest is window dressing. If it becomes just an airshow without the defense heavy metal, then it can go anywhere. If the heavy metal & defense exhibitions stay, then it must be Sydney, Melbourne, Canberra.
If 2015 is the last year, that might co-incide with RPT ambitions of LINFOX. I think the only other airports that will take heavy metal, but not disrupt RPT will be Military ones. Richmond, East Sale, Williamtown. Woolongong might be an outside chance.
Its hard to see where you'd put a display "box" at Richmond. Williamtown & East Sale are a long way to transport VIPS (the tender is out for buses & limos for government VIPS at Avalon - you should see the list!). Woolongong would be good except the runway is probably 300 - 400 m short.
The other option would be a tag team with 2 airports. Moorabbin / East Sale or Bankstown / Richmond. Put the military heavy metal at the military airport and everything else at the civilian one and do flying displays over the civilian one.
Or it could get too hard. I have no idea of the numbers, but it wouldn't surprise me if the civilian & military parts are each not viable as separate entities.