The Square Enix owned studio is apparently already working on a new unannounced 3rd person action-adventure title that will be targeted at both the Xbox One and PlayStation 4. LinkedIn profiles of some of those who work at the studio have already been updated to reflect the change.
According to what we are hearing, the major work on Thief was completed around the end of November of 2013 and the studio starting rolling developers off of that project and on to the new unannounced project. It is believed that the new project isn’t the game that was cancelled in October of 2013 according to sources claiming to be knowledgeable. It is also unknown if the game is planned to be announced at E3 in June and of course we can only guess, but we suspect that the new title is targeted for a 2015 release.
In addition to the new unannounced title, the studio is also working on a new next-generation Deus Ex title as well.