I see that a member of FSU now is saying that the location of Skate DownUnder has been changed to a rink in Sydney.
http://www.isa.org.au/ so far does not seem to have any mention whatsoever of Skate DownUnder, so I can neither confirm nor deny Sydney vs. Brisbane.
But the person at FSU seems well-intentioned and well-informed. I do not see any reason to believe that what s/he posted is not accurate inside scoop.
I will go back and edit my post that mentioned Brisbane above.
ETA: As of May 23, the ISU.org calendar listing now officially indicates Sydney as the "New Venue" for Skate DownUnder.