The current A380-800 is approved for a maximum 538 pax on the main deck and 315 maximum on the upper deck making a grand total of 853 pax.
With a pax mix of males, females, children, infants, baggage and catering a 853 pax load may be a problem due to the ZFW limitation.
A 853 pax load may be available with a stripped down aircraft and little in the way of pax amenities.
Perhaps Keg could advise what average payload is available on the QF fleet as a rough guide.
An A380-900 or A380-1000 are just for virtual airline dreamers !.