I think it's likely that Qantas is seriously looking at buying 5-6 747-8I's to fly between Sydney and Dallas and possibly from Sydney all the way to Johannesberg in South Africa.
Why stop at that number. DFW is American's largest hub and is just one stop away from most cities east of the Mississippi. QANTAS could divert much of the North American traffic that currently requires two connecting flights to DFW and require just one connecting flight. DFW has a brand new international terminal that is mostly empty. LAX is very close to capacity. If the DFW-SYD flight works out, why not add a DFW-MEL flight? With the addtional range, MEL-SFO should be easy.
The only restriction on flights between SYD and JNB is ETOPS - a 747-400 could fly that route today if they were so inclined.
SYD-JNB is already nonstop both directions with a 744