Haha, no, this one you can be 100% sure. I don't think a pax version has gone there loaded once in years. SYD and the 747 is not like an occasional regional (painful) swap that everyone hates. The reason is that they have an enormous inventory of aircraft that can make the SYD range - their regional-configged A330 aircraft. If they are forced to, they can press on a regional frame into service, which there is far more slack with in the scheduling than with the long-haul aircraft (and a far less opportunity cost than swapping out a 747 from a regularly-scheduled long-haul route). There would be absolutely zero reason for them to swap a 747, it would be economically pointless. The only way you're going upper deck to SYD is if you get on the freighter, or crack into the crew rest area.

the only last minute switching that may occur on the HKG-SYD route will be between an A330 with the new cirrus business class and an A330 with the old coffin business class.