For every player aswell, from level 1 to 70(80) scaled, so the same concept as the Soup and the Siege, but this time around it happens all over Azeroth.
While the world gets updated it needs a solid reason for us to revisit it aswell, why not update it to look like the norm of todays expansions, have us all hyped with the new graphical update + content.
To make sure the revamp/update isn't for small part of the game, make the game all about the whole World. Best way to do it with WQ popping up all over the world but also with events happening at random locations, maybe once Goldshire, then Kharanos, durotar, everlook, etc.., having to defend it from assaults or doing special unique stuff like the soup? maybe farming.
Same concept i would suggest with a caravan going around place to place that sets up from town to town, like Darkmoon faire but then better made.
Would this spark a world update/revamp even more for you? And this shouldn't be just for the end game players, these kinda events should be available since level 1. Just scaled.
I don't think WoW needs new zones, we gotta have an updated world with todays standards and one solid storyline that is up to date.