It looks like the Big M is jumping back in the PC game, as Microsoft Studios is currently seeking a senior engineer to join the company ranks to help "build a new title based on a beloved franchise for Windows 8."
There aren't any hints as to which franchise the listing is in reference to, but the post notes that the studio "is focused on building a robust and highly scalable cloud service that is central to the game experience."
As far as "beloved" franchises go at Microsoft, the list is rather thin, so it can't be too hard to guess what it might be. I'm hoping it's Halo, but it could very well be Forza Motorsport or Fable as well. What do you think this "new title based on a beloved franchise" might be?