In my opinion, if Guild Wars 2 lives up to the hype (it is being designed for all manner of player), then we will officially farewell the World of WarCraft franchise. Guild Wars 2 is subscription fee, and the only money required is when you buy the game itself. Not only that, but Guild Wars 2 will pioneer the "MMOlution", and if it doesn't succeed, surely the Next Generation MMOs following it will.
Personally, I believe this next expansion will be the last of World of Warcraft, and they will probably re-ignite the marketing wheel for Diablo III and concentrate solely on their 'Titan' project.