Actually they way they are dealing with it is focusing on Legion and trying to not make it a WoD II. They've lost 95 million subs over the years, I don't think they are worried as much about the tiny amount of those that are clamoring for legacy realms. They'd be better served to make a damn good Legion expansion and get people to come back to that. If Legion is amazing it would get far more people coming back then retro realms would IMO. And you know Blizz would toss more support Legion's way than any retro realm.