I found some information concerning if there is an upcoming new starcraft.
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Looking for programmers experienced in StarCraft
Blizzard.com has job advertisements looking for a "Game Balance Designer" with experience in StarCraft and Warcraft 3 (this could mean that Blizzard is working on another RTS though).
On August 2, Blizzard began looking for "Level Designers" with "experience building levels using any popular 3D Real-Time Strategy game toolset." Such toolsets were used in Warcraft III, and it has been speculated that a Warcraft 3-D engine would be used for Starcraft 2. Blizzard has said that the job is for work on a RTS, but has not said what the RTS is.
But blizzard is hiring though.
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6 February 2002, Bill Roper in an interview with InsideMacGames.com:
"I promise Blizzard Entertainment will make StarCraft II at a later time."
And he should know cause he does the voices for most of blizzard game units.
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On the site for the former game (indefinitely postponed) StarCraft: Ghost's FAQ:
Q: Will there be a StarCraft II? When?
A: Although we have not made any announcements and do not have a development or release timeline, we do fully intend to revisit the world of StarCraft on PC at some point in the future.
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Actions seen by fans as indicating possible work on a StarCraft sequel - as well as the more obvious pointers above - including a hidden mission in StarCraft: Brood War, the lack of other projects for Blizzard after World of Warcraft's completion, an Easter egg unlocked after completing Warcraft III on the most difficult setting , as well as a leak about a 2007 release from HanbitSoft, the Korean publisher of StarCraft.