MMO is where the money is. Wouldn't surprise me if it ended up being MMO, anyway.
Blizzard can not handle maintaining two different MMO's at the same time. You have to look at business capibility as well. Not to mention that StarCraft has made them so much money because people buy other Blizzard games just because of how good StarCraft was. They would not risk displeasing those people. Not to mention that they left the storyline in a cliff hanger. If they follow the same trend they did with WarCraft then they will have to end it without a cliff hanger before moving on to an MMO.
StarCraft 2 and Diablo 3 are being made. There have been subtle hints that Blizzard has been purposefully leaking without announcing it. Like I said before announcing it is what screwed Ghost over. I've found articles about Diablo 3 music being made, and with how StarCraft ended and how much Blizzard has been making off of it, it's inevitable that StarCraft2 would be made. Considering how StarCraft is starting to lose momentum in Korea, I'm guessing they'll do StarCraft2. Not to mention that they're still having problems with Blizzard North since their members ditched to make Guild Wars, so it can't be Diablo 3 yet.
Around a year ago I saw Blizzard post job openings for level designers for RTS games and RPG games similar to Diablo's style. Right now they just posted MMO jobs that means in around a year they'll probably announce something MMO related. It's their way of hinting at things to come.
