Or you know, have Azuremyst and Silvermoon be relevant on an expansion lorewise.Knowing how Blizzard works, if they were to go through with any potential Ren'dorei vs. Sin'dorei story, they'd simply reduce it to a scenario set in Quel'danas like they did when Alleria went to the Sunwell or in the final part of the Blood elf Heritage questline.
Since Quel'Thalas gameplay wise exists in the Outland world, they would have to rebuild it from scratch in the Azeroth map first to update it (or in its own map anyway if it was scaled to a continent like the BfA islands), at which point they might as well just create a new land from scratch.
I know it's cool and all to drool at how Quel'Thalas is meant to look like lorewise, but realistically they will not update it and do it justice. They haven't touched it since 2006. If they wanted to update it, they would have done it in Cataclysm.