Supererogatory unearthed what appear to be two juicy bits of information about the studio. First up: Apparently Firaxis was developing a sequel to Civilization Revolution back in 2008 for PC, PS3 and 360, according to the resume of David Jones, a current character artist at Firaxis.
Also of note, the LinkedIn profile of ex-Firaxis level engineer Chris Doyle and the resume of former game programmer Will Miller both reference an "unannounced," multiplatform title, using Unreal Engine 3, as being in development at the Civ studio. Perhaps unsurprisingly, Miller's resume classifies the mystery game as a "AAA strategy title." Supererogatory posits that it could be the same title that was first spotted on a resume from 2008. We've yet to get a response from Firaxis or 2K Games on the matter.