I'm no marketing guru, but it would appear to a lot of people that current WoW and Vanilla WoW were aimed at different parts of the gaming market overall. Or at least, what appeals to the legacy crowd is often touted as not existing any more in retail. Would it not be possible to seperate them in terms of advertising; maybe releasing legacy stuff under the name "Age of Warcraft" or sometihng (yah, you can tell I'm no marketing guru).
So you have World of Warcraft for the more immediate ARPG experience, and Age of Warcraft for the slower paced RPG style. Could even allow them to persue the "casualisation" of retail (sorry couldn't think of a shorter way to describe the direction since TBC, yes it isn't ideal, but I hope you get what I mean); while having an alternative to offer the more "grindy" crowd