so with Treasures of Voldun I run into that Grayal's Last Offering is closed until one has progress enough. Most likely The Fall of Emperor Korthek, but thats a Horde-only quest, not sure how it is for Alliance.
In any case, if it's linked to faction specific quest line, so there might be a need to have hide_before for each faction.

Thanks, I have only one horde character and it's highly unlikely that I'll ever level another one. :)

Assuming it's needed, I'd just do a faction="Alliance"/faction="Horde" version of the point with veeeery slightly different coordinates and a different hide_before.

Then there is not even a need for a special tag, just two records.
Do you have Alliance character that's questing through the area to test that chest?

I do have an Alliance character who hasn't been there yet. I'll check it out when they have the opportunity.

"Alliance players can now access all treasure chests for Treasures of Vol'dun."
https://worldofwarcraft.com/en-us/news/21973195/hotfixes-august-22-2018

I think they refer to this chest.