I would endorse WoW 2.0 if that means a new engine. Just making higher graphical leap (which often is tied to new engine or newer version) isn't really what's needed. WoW and Blizzard games are more about aesthetic fidelity rather than graphical marvel on the technical level.
I do feel the engine really hampers down the MMO aspect though. It can't really handle 20-30 in worldPvP situations. Considering games are proven to be able to handle more players like that and I don't think blizzard are bad to not be able to make it work considering HotS and Overwatch works great on the network side. Only thing I can think of is just that it's still an engine from 2004, obviously it has gotten updates, but the underlying framework is still old.
A new engine and emphasis on being able to handle more players is what would make me think WoW 2.0 to be worth it.