hmm...I thought Qantas did sell premium economy on MEL-PER (QF9) and SYD-PER (QF5)? At the very least, you can certainly upgrade with points into W from Y on those flights.
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hmm...
Expert Flyer says they do, but there was also an article recently (either here or on ET) that said they didn't.
I flew Mel Perth and return pre Covid in W if that is Premium Economy