This is something I learned about after Googling the term "windows 8 xna updates", which yielded results of no news on such a thing.
http://monogame.codeplex.com/
You read it right, it's an actual port of the XNA framework utilizing the powers of OpenGL, thus ensuring XNA games can run on iOS, Android, OS X and Windows 8's Metro interface. It's based on the current 4.0 release of XNA, though from code examples it looks as though some parts are vastly different from the "canon" XNA.
Has anyone here used it yet? I'm considering trying it out if in the next year Microsoft say nothing on XNA. It looks very encouraging as a backup should Microsoft abandon their own system.