A better replacement for the Qantas 747-400 would have been the 777-9 as it has the same passenger capacity as the 744 with twin engines.
After Qantas got their a380s they have been moving away from larger aircraft on the whole. The new 789s have largely replaced the old 747 routes and the new order for the for the a321xlr look like they'll replace a few of the a330s.
Part of the reason for the VLAs in the past was due to CASA preference for more than 2 engines and the main base being Sydney. Now with more importance in other bases and CASA not being as strict on twins (EDTO), the need for larger aircraft is smaller.
I don't see Qantas ordering too many 777-9s in the next 8 years, due to the current a380 refurbishment programme and the overall migration to thinner routes.