The JNB - OZ route is fairly strong - but mainly to SYD. Qantas left the JNB-PER to SAA with a code share and that has one A340-300 (I think) per day. Mostly, folks go to SYD and then spread out. I guess there are options to go to SIN (or neighbouring) and then down to OZ if that suits. As it happens, I'm researching JNB-PER and the options (for what I want) are not good.
In the past, BA had used their 747s to go on down to DUR or CPT after a suitable 'bounce' at JNB. Then the machine returned to JNB in time for the main haul north. However, they then bought Comair and that did the trick.
Many of the european carriers have looked at Tag-ons from JNB and daylight returns. In the end, the greatest majority opt to leave the machine parked up for the day on a remote stand. But the main carriers all love the route. Personally, I've enjoyed daylights in both directions very much.