My zone: Void’thalas
(maybe the name could use some work)
We would need some sort of driver for this revamp. Cata had a big revamp, and the driver of that was Deathwing causing havoc. I guess each person can imagine their own driver for their revamp.
I would start with the last Patch of Shadowlands. We pretty much solved the Jailer problems, and return to Azeroth. Alleria and Turalyon assault Quelthalas, while Liadrin is tasked with defending it. The last Patch of Shadowlands could end with Alleria turning the Sunwell into a Voidwell, pulling Quelthalas off of the map entirely, and sending it to the Void. And that could be how Shadowlands ends.
The revamp could come in the next Expansion. Maybe the Alliance and Horde want to investigate the incident and rescue any survivors, with the bulk of their militaries there during the event.
So, one of the zones of the next expansion could be Quelthalas consumed by the Void - but its magical properties keep it mostly intact.
We could have Alliance and Horde bases from the initial assault acting as our hubs, once our Champions get deep enough to make contact.
Regions can remain untouched through magic - the Light or the Arcane, or both, warding off the Void. Other areas can be totally warped by the Void. The Ghostlands could be totally warped into a Voidish wasteland with zombies.
And it could be one aspect of the expac, not the whole thing. Maybe other stuff is happening to cause revamps all over.