Once normal line ops start I don't reckon you'll see S/Os on the MEL- PER- MEL sectors. Simply no need for them.
All depends upon how the rest of the rosters are built. As a MEL-LAX or SFO flight would be around 30 hours it would could well mean that these flights (Perth) continually hit the 30/7 limit. You'd three days at home after a US trip before the hours limit would disappear, but these trips only have a min of 2 days MBT. The same issue will arise if the Melbourne 380 people are supposed to fly to Singapore 2 man crew. It can certainly be fixed if you put SOs on ad hoc, but that would quickly run the resources down. It's messy scheduling, but then I guess that's the norm anyway.