Firaxis, the Sid Meier led studio that most recently brought us Xcom: Enemy Unknown and Civilization V will reveal their next project at the upcoming Gamescom expo in Cologne next month. No further information on what to expect is available, not even possible platforms.
Potentially the studio could revisit previous titles like Sid Meier's Pirates or Sid Meier's Railroads, or even the sci-fi take on Civilization called Alpha Centauri. But it could also be something brand new.