Don't get too excited but there might just be a Thief 4 trailer through the br- hey, I wasn't done talking.
Gematsu claims to have captured this 30 second cinematic trailer from a demo reel attributed to lighting and compositing artist Eric Wong, but that it was hastily edited out.
The artist's site states the demo reel hasn't been updated since August 2011, which suggests the trailer may have gone undiscovered since then. If that date is accurate and the trailer is genuine, then the cinematic may have been produced as part of Eidos Montreal's internal conceptualising or pitching process rather than for inclusion in or promotion of the finished game.
We're still waiting on a full reveal of Thief 4 but Eidos Montreal seems to be getting chatty at last.