Maximum in a 28 day roster cycle is 3.5
If you operate a BNE flight then this number will be reduced as this pattern is a minumum of 6 days.
Rumour is that the direct MEL is being reconsidered, and a/c 4 will be redeployed to JNB. I believe these will initially be via PER due to ETOPS.
It is more expensive to keep the a/c on the ground in SYD than to do a SYD-MEL-SYD. The service will be very quick ad simple. Tickets will be sold in Y and W, but not in business. It is unlikely that many people will specifically purchase this flight, as they will have to check in at international 90 minutes prior.