I would be slightly careful before dismissing XNA so easilly.
Ultimately XNA is an abstraction on top of DirectX9 and DirectX11 - if there are technical reasons why XNA can't work on WP8/WinRT, I suspect the XNA team will overcome them with a new abstraction layer so XNA "just works" for WP8/WinRT.
It would certainly be retarded if Microsoft dropped support for XNA only just as it starts to take off - and particularly whilst it is the only real indie-development platform for XBox360. Arbitrarily preventing Xbox indie-apps from working on Win8 when they have such a dearth of good Win8 apps would be pretty special.
xna seems to be a mess, I have not seen much support for it and when they do update it it's way late, and xna games for windows has issues with having to use the MS game network stack.
xna seems like an idea that could be great but has been left lingering on the side.
if they are going to update it yet again they need to put a lot more work into really supporting it and making it worth the time to learn.
or unity 3d will just take over....