This warning ONLY comes up on multi-sector flights where one of the sectors isn't sold as J (eg MEL-PER-KTA, eg MEL-SYD-BNK) - if you book PER-KTA or SYD-BNK directly you cannot buy J, but you can with a multi sector booking. This now matches the way Qantas do it.
Virgin will not warn you about pretend J E190 flights (hard product 2 Y seats, soft product J) as they consider them J. They aren't J. It still remains caveat emptor with regards to E190s until the refit is completed.
Having flown both Virgin pretend J E190 and Qantas 737-400 J, there is no comparison between the two - given the choice, I will pick Qantas 100% of the time.
Virgin, whilst getting better, still remain more inconsistent in service delivery than Qantas.