MGSVancouver.com. The studio, which seems to be called Zipline Studios, is focusing on "building a world-class development team in Vancouver, BC, Canada, dedicated to making games for core gamers. Our mission is to push the limits of proven and unexplored game development and show the world what's possible on Microsoft's game consoles."
After a bit of investigating from members of the NeoGAF forum, the website of an MGS Vancouver team member was discovered, detailing what he is currently working on. His resume states that, as a member of Zipline Games since February 2008, he has been an "original team member in a new studio with a start-up mentality, hiring a team of artists to create social microtransaction games. Over the course of the year, our studio strategy has changed and now focuses on developing a core AAA shooter experience using Kinect."
Although it appears that the studio has been around for a while, it has only had a public face for a month or so. Like most of Microsoft's internal studios, what they're currently working on is largely a mystery. Could this be the first hybrid Kinect game, utilizing a controller? Given the timing, we'll probably know a lot more next month at E3.