The problem of PB is so out of hand, general pax know it isn't enforced so just use the PB queue. Case in hand, in SYD. Got to the gate and there were two almost equally long lines. I walked to the front to see what was going on and sure enough, one was the PB line. Walking back towards the end I actually asked a couple of people of they were meant to be in that queue. Their reaction made it pretty clear that they weren't but could have cared less.
I 100% blame Qantas for this. People know that their are no repercussions for using either queue, so they just do it. Knowingly.
Perhaps all people in the lounges should just sit around and wait an extra 10 minutes before heading to the gates. Eventually when QF have had enough of their flights leaving late due to priority pax being late to board they'll land up doing something about this mess.