JNB-SYD flights on QF are permitted. (It crosses the Indian Ocean)
So there should be nothing incorrect about JNB-SYD-HKG-LAX-JFK-LHR-JNB.
Equally JNB-HKG-SYD-LAX-JFK-LHR-JNB should also work.
However you will need to purchase an xONE5 ticket in both cases.
Happy wandering.
Fred