"Games for Windows brand is dead btw...They have an Xbox Games section in the Windows 8 app store and I can see them doing some synergy with that on the Xbox."
Depends on how you look at it. I still see new games being released so its not dead. As a means to jump start the service could be this method to stream your games to the new X1.
It should be very interesting to see what functionality MS do include with the Miracast support. MS definitely can tie in their products together to make a tempting proposition for PC gamers. Basically this would be MS steambox. As was rumored, Steambox would be able to stream your PC games to your TV. MS could basically head that off using Windows Blue and the X1. Also as Zappykins has noted, MS would probably be able to stream all of your DirectX PC games to your TV making its Miracast ability a killer App if they go down that route.