The very useful post by Forward CofG got me concerned, because I for one had been looking forward to the flights. Just how marginal are the operation economics?
Assuming 180 min ETOPS (or ETDO), the approximate distance is 6444 nm. Total fuel needed I calcuate as 109.6T with standard holding fuel.
I calculate that at 15 degC air temp, 318.8T takeoff weight, they can get off with 348 pax (which is no problem in a 361 seat config) and basically nil cargo. With 30 deg 302.8T T/O weight, it is down to 206 pax which is not acceptable. All at nil wind.
So it will have to be the old middle of the night departure from JNB trick. Much beloved of underpowered early model 747s. By the middle of the night, it has cooled down in JNB with the altitude helping considerably, and hopefully there is some wind, and hopefully Sydney has no bad weather requiring more holding fuel. Of course, Perth is always close by for a tech stop, and ADL and MEL for diversions. Should make it reliably, but I think it would be a much better operation coming to/from Perth than Sydney; no prizes for guessing where I live.