Valve planning something for Xbox 360...episodic?

Valve announced today development of future game releases for Microsoft's Xbox 360 console, with the first (unnamed) title "coming soon." Valve's Gabe Newell said, "The combination of Source and the 360 provides game designers the chance to create powerful entertainment experiences...Whether developing a traditional FPS, RTS, RPG or delving into new genres, the Xbox 360 is a great platform for expanding Source and our game experiences.”

Of course there is no mention of what this mystery title is, as they're undoubtedly saving the big reveal for E3. But what could it be? We know Microsoft is interested in episodic distribution (Peter Moore told me so himself) and that Ritual is interested in bringing their Source-based SiN Episodes to the 360 (they've said so), so it seems a reasonable assumption that Valve could be bringing the episodic efforts of SiN and Half-Life 2 to the 360 platform, with Microsoft making the big announcement at E3. What say you Joystiqers?

[Thanks, Nate, Jeremy, and Crimson]