[Update]: After a being asked on Twitter (via IGN) whether or not this tease has something to do with Fallout, Bethesda's Pete Hines replied, "You talking about the Vine thing? Guess again :-)."
So it looks like we can rule out Fallout 4.
[Original Story]: Yesterday, Bethesda announced that their time with Skyrim has come to a close and that they are focusing on a new project. Today, they posted a video on Vine teasing this project.
Speculation has continued that this means they are working on the next Fallout game, but Eurogamer has suggested this could be the next Wolfenstein or even the code-named Project Zwei, the survival horror from Shinji Mikami.
What do you think it is referencing?