QF has a 747 replacement. It is called the A380...
TBM, unfortunately, the A380 hasn't turned out to be a good B747 replacement which is why AJ cancelled the last 8 that were ordered and, consequently, some of the B747 fleet will remain in service longer than originally planned.
The absolute "stand-out" replacement for the B747 & A380 is the B777-9X and I see QF ordering it for entry into service in 2019 with ongoing deliveries replacing the B747's and then the A380's. I expect the B747 to leave the fleet circa 2020 and the A380 circa 2022-2023 by which time, most of the fleet will be more than 12 years old and thus will be written off.
At the same time, the A330's will be replaced by B787-9's so that, by 2025, the QF International fleet will consist of only B777-9X's and B787-9's (with possibly a few B777-8's & B787-10's for select routes). With both types having a common endorsement and some engineering components in common, there will be significant savings compared to the current fleets.
The A350 has been getting good reviews but I believe the B777-9 will have lower seat mile costs and the commonality with the B787 will sway the decision in favour of an all Boeing fleet.