The G rego will remain until CASA grants the AOC, something to watch for if that AOC is getting close is a large piece of masking paper covering the new aust rego. When the AOC is issued the paper will be removed and the G rego will be quickly painted out. The aust rego needs to be on the aircraft prior to the AOC being issued because casa like to measure it up, make sure i's the right size, right font etc.
I have heard that the aircraft has been put into a storage program due to the time they expect this to take.