Olivier Bloch brings the good news:
MS Open Tech has been working with many open source technologies to help Web and C++ developers extend their reach and have their code work seamlessly on Windows devices.
You can now integrate your code using Cocos2DX, Cinder, Ogre3D, Box2D, Bullet, OpenCV, or Angle to a C++ Windows Store app project and rapidly get your app or game running on Windows 8 and published to the Windows Store.
Sweet, I want to play with Bullet. Also relevant: Developing games docs.