What then happens to pax coming in on the  aircraft from MEL? If the flight has departed MEL Int, then to use the  lounge, they would have to come in through immigration, go to the  lounge, back out through immigration and reboard. Not worth the effort.
Of course, if the MEL-PER is actually a flight that has departed MEL  Dom, then everyone just alights as a dom pax and goes through  Immigration in PER. But if the lounge is landside (as it currently is)  then you'll have to do the whole tiresome immigration thing after  leaving the lounge.  (Yes, yes, I know that's what happens in ADL, but  QF is clearly talking about a much bigger operation in PER).