From what I have heard it wont be.

Was chatting to someone related to a Microsoft Studios employee about Bungie and MS parting company and from what I was told Bungie wanted to jump right in and do Halo 4, but Microsoft didnt want them to do it just yet as Halo Wars is out next year and then there is the series of Halo games by Peter Jackson so Halo 4 would just be Halo overload and people may get bored of the whole franchise. So I asked the obvious question with the team that did Shadowrun closing, Bizzare being bought by Activision and not MS and now talk of Bungie flying solo are MS quietly withdrawing from the console war. I was expecting a yes, but got told instead that its full steam ahead for xbox and top secret musnt tell anyone its the big axe for Games for Windows. There are no plans to develop any more games for PC once the current crop are finished, Piracy is costing the industry too much