QF already has 4 Internationally configured 332's. They could do Per-Jnb easily range wise but not direct.
Operating PER-JNB doesn't make sense when QF are already code-sharing on the SAA services. Also, the passengers from the Oz East Coast don't want to fly via another port. QF Scheduled Block time SYD-JNB 14 hours, SAA Scheduled Block time PER-JNB 11.05 hours - when you add a SYD-PER sector with a transit on that, it means a much longer time for the journey.
Also, the A332 capacity is significantly less and the B744 services have been experiencing very high load factors so it's not the aircraft type to consider as a replacement. The way the loads have been steadily increasing, the aircraft that might be considered is the A380 but as we all know, QF aren't taking delivery of any more of those.