See CX.com. As of 24/03/09 Hkg summer schedule has 3 types doing JNB:
744 x4 p/w
343 x1 p/w (no long lay over due to becoming acclimatised - PX)
777 x2 p/w
So it would seem that its not just JNB engineering that would like it to go there, but planning dept too.
According to basings office "no more temp bases available in JNB" so much less the chance of a permanent base.
AFL