>>Not sure if this answer the question but this interview talks a little about it.

Thanks for the link. Here's the wow moment for me: "Windows 8 actually highlights a problem with Windows Phone 7. The Windows Phone 7 API supports managed code only, with two application platforms. If you can’t get your XAML-based Windows Phone 7 program to run fast enough, you can try rewriting it for XNA, but with XNA you’re still using a managed language and you’re still going through a managed API. And if you can’t get your Windows Phone 7 XNA program to fun fast enough, you’re stuck. You’ve hit the wall."

Wow. Who is going to want to spend $ on WP development after a glowing endorsement like that from somebody who used to do a WP column and now is doing C++ and DirectX that he says he'd like to see translated to WP to help overcome the risk of sluggish UI. For real- C++ UI to prevent slow managed applications making you hit the wall?! Sounds to me as if an emperor has no clothes.