I get why this is attractive to people who plan to still play the latest expansion of WoW. You did something cool and rare no longer in the game and would like to show it off.
For just a minute, consider the very toxic behavior it brings to Classic if farming unobtainable appearances is a reason for players to be in the game.
It doesn’t just potentially hose the server economy beyond repair, but has the potential to ruin the raiding experience entirely.