I've got to agree, I hope they don't go nuts with expansion packs. Look at a game like Everquest, which used to be the King of MMOs, but severely lost its quality after the first 4 or 5 expansion packs and then became a joke after the 10th! http://bit.ly/f7zVsd

Thing is I think Blizzard know this. There is still one unnamed project in Blizzard development alongside Diablo and SC2, and ill bet anything its a new shiny MMO. Whether its Warcraft or not remains to be seen, but i really wouldnt be surprised if by the we get to WoW Patch 3.5 or whatever that there was a new Blizzard MMO on the horizon.
http://bit.ly/foMYQL

I'm guessing WoW will be like Halo 2 or Starcraft. People still play those games, because they were well made and inexpensive to play, even though there are newer games out there.
http://bit.ly/eeZHSn