Had my first QF Op-Up on a BNE-SYD A330 yesterday..!
3 days before only a handful of seats in J sold, and Y was light too - so much so it was still on the initial fare bucket ($185), while other flights were higher.
Got the beep at the gate and it totally shocked me - when I saw the green 3F I realised what was happening but my colleague was confused and worried about our booking. Quickly checked the seatmap after boarding and J was full, Y had about 4 seats free (on an A332..). Don't know if they cancelled another BNE-SYD flight or if it was just massively oversold at the last minute, but I wasn't complaining!
NB Colleague had the time of her life, it totally made her day - still amazed (and probably a little thankful) I had her on my booking.