Well the AUD224.00 for PE was a 40% increase over the Y price of AUD552.00 (travel was CAN-HKG-MEL).
And according to my maths a CX Y+ seat has a footprint on the aircraft floor that is 125% of a regular CX Y seat so PE fares of ranging up to say 130-150% of regular Y fares are acceptable to most CX customers. (based on typical CX A330). And, just for comparison, I also worked out that VA B777 Y+ seat footprint on aircraft floor is 125% size of a regular Y seat on VA.
For QF assuming A380 I found that a Y+ seat has a footprint on the aircraft floor that is 143% of a typical QF Y standard seat, so in QF's case you would expect to see Y+ fares being 140-160% of regular Y fares, maybe up to 170% at a stretch if you believe the on-board Y+ product is non-stop caviar and champagne.
And then just a quick glance at the official QF CX and VA site sale fares where its possible to compare Y and Y+ fares we see:
QF SYD-HGK return: Y = $808 vs Y+ = $1399 (so Y+ seat coming in at 173% of a regular Y seat)
CX SYD-HKG return: Y = $958 vs Y+ = $1905 (so Y+ seat coming in at 198% of a regular Y seat)
QF SYD-LAX return: Y = $1299 vs Y+ = $2999 (so Y+ seat coming in at 230% of a regular Y seat)
VA SYD-LAX return: Y = $1305 vs Y+ = $3126 (so Y+ seat coming in at 239% of a regular Y seat)
First of all - this tells us about different markets, obviously for longer flights then Y+ becomes more attractive for passengers and so probably results in airlines able to ask for more $$$ for premium economy seats. But it also hints that either QF are not filling their Y+ seats at those prices, or alternatively, if they are, then Y+ must be more profitable than flying bog standard Y seats, even if they have a competitor with Australian costs (like VA) or a competitor with lower costs (eg CX), and also very interesting to note that CX can command such a price premium for their SYD-HKG services.
In short - if QF predicts that there is little demand for premium economy, then given QF's track record, I can confidently predict all of QF's competitors will eventually install Y+ seating and proceed to hand QF their own a%$e to them.