Last week’s Worldwide Invitational unveiled another project Blizzard has under development, in addition to Starcraft II, World of Warcraft: Wrath of the Lich King and Diablo III. The question is: what could it be?

As it appears, Blizzard has a fourth development team working on something, which may not be connected with any of the above mentioned games, but Blizz executive vice president Rob Pardo didn’t mention what it was.

It still remains unclear whether Blizzard is planning a new addition to an existing game (a successor for either World of Warcraft or Starcraft) or a new franchise to add up to the enormous success the other titles have had.

During the Worldwide Invitational, Paul Sams, chief operating officer at Blizzard Entertainment, told Gamasutra that Blizzard doesn’t exclude the idea of another MMO if the idea is right and they are able to come up with a gameplay experience that would be appropriate for an MMO.

Sams also added that with three of the best-selling franchises of all time preceding it, a new franchise would have to be equivalent or better than what they’ve done before. The challenge of course would be figuring out what that other franchise might be.

The idea of releasing a new franchise is there: “Are we ever going to release a new one? I would absolutely say we will at some point.” However, Sams also added, when that day will come is just something he doesn’t know yet.

In the meantime, gamers can sit and wait for the events that have been confirmed so far: the World of Warcraft expansion, Wrath of the Lich King, whose official release date is yet to be made official, but many believe to be this year, Starcraft II, whose release date also remains in the blur, and the highly anticipated Diablo III, which should also kick in ... when it’s ready, as usual.