XNA is already available for windows 8.x via the open source MonoGame project. In fact MonoGame has had support for Windows 8 for over a year now. So if you like the XNA api, it lives on in the OSS world.
While XNA is not available on Windows RT the open source monogame project supports the XNA 4.0 API on windows RT and Windows 8. A number of games in the store already use this (!ARMED and Draw a stick man epic adventure for example)