As much as i would like a world revamp, it's just not worth the effort.
Sure, it's a cool idea because we get to see how a lot of places evolve, both visually and lorewise, but in the end is a massive amount of time and resources for very little gain. As leveling zones they are no longer needed since they can just use more recent content as the 'basic' leveling experience. As max level zones the game is simply not built to support a whole max level world in a dynamic an interesting way... so basically there is no point on doing it. I guess we'll get some zone from time to time when it makes sense, but that's it. Honestly though... sometimes i hope that internally something like 'wow 2' is on the works with a new engine that allows a more dynamic use of the world.