A WOW with better graphics.
Do you think that would be a good business for them? I'm not sure how'd they could do it without fracturing their existing playerbase, which would not be good for either Blizzard or the players.
I think "WoW with better graphics" is an MMO genre best left to their competitors. There have been a few contenders in the last few years, but all of them failed to even approach WoW's success. I'm not sure "graphics" are why people play WoW or that "better graphics" are enough to convince WoW players to move to another game, even if Blizzard themselves made that game.
Now, I could see them potentially having success with a new non-Warcraft based MMO IP. If the rumored "World of Starcraft" ever materializes, I'll be there on day one.