Many fans and developers were rightly excited to see Microsoft announce native coding support for Windows Phone 8. Microsoft even went on to dedicate a significant chunk of the latter half of its WP Summit presentation to the gaming in the new platform, which has gained the most from the addition of native code.
Then a notable question popped up: where does XNA fit in? For those who don't know, XNA is the development environment that makes Windows Phone gaming possible on devices today. However, it's considered a sandbox that only gives developers a set of tools to work with rather than direct access to the guts of the phone itself. There was zero mention of the environment at the WP Summit and once again there wasn't much to see in the Windows Phone 8 SDK leak.
All About Microsoft's Mary Jo Foley has raised the question as well, and has dug up enough evidence to get a few theories going. While the leaked SDK documentation and Microsoft officials suggest that XNA will be fully supported as a way to code games for WP8, there are people who say otherwise. Most notably Chris Walsh, a team member of ChevronWP7, claims that XNA will be supported and will benefit from the improved hardware, but it won't have access to the same high-level code that the native C++ will provide since it will run in an "isolated mode".
In other words, XNA will probably be there as a less powerful alternative that also serves the purpose of backwards compatibility with Windows Phone 7.x games. For right now we still have to consider that a rumor, since Microsoft itself hasn't discussed the topic in-depth yet.
Source: All About Microsoft, Chris Walsh (Twitter)