Support for C, C++ native code in Windows Phone 8
thenextweb.com
thenextweb.com
http://blog.chromium.org/2010/03/introducing-angle-project.h...
For games, windows phone doesn't support opengl es. So you still need to rewrite some code.
It does look like someone is already experimenting with an OpenGL ES implementation over XNA, so we might still have access to some form of OpenGL on WP: http://www.straightforward.se/storyserver/opengl-es-support-...
The Game problem can be solved with game engines. But I'd like to write opengl directly.
As for UI, Qt for android is a good approach.