How fast are solutions like VNC or Citrix? Could you run a VNC client on your RPi that connects to a VNC server running on a Windows box? Would this be fast enough for realtime video? And will VNC show Silverlight video or does that not work due to DRM type of stuff?
What about PlayOn which kind of re-encodes web based content like Netflix, Hulu, etc to stream to other devices? It only works with SD video, not HD, but is this a partial solution? It works with pretty much all DLNA compatible devices. And it seems to run on a bunch of media streamers, some of which have similar hardware to the RPi.