I could see somewhat of a revamp/update happening to WoW, but nothing on the level of ARR. Square-Enix had to do ARR or close out FFXIV, it was that awful beforehand. WoW doesn't have that problem, they still have lots of people playing even with the recent in-game issues. There's still stuff they can work with, they don't really need to start from ground zero. They stand to lost a lot more than they'd gain with such a system, many of their players are at least loyal enough to come in at some part of the expansion & are very connected to their character's mounts/pets/look/etc. Redoing the entirety of the game would only serve to give these people an excuse to never return if they didn't like it immediately upon logging in.