I have recently found out than ANGLE (Almost Native Graphics Layer Engine), supports DirectX 11.
ANGLE is developed by Google as a WebGL provider for Chrome. It is a Khronos-compliant OpenGL ES 2.0 implementation built on the top of DirectX 9 or DirectX 11.
I think integrating it would be a smarter approach to bring Cocos2D-X to WinRT platforms, since it would save a lot of time abstracting/replacing all the OpenGL calls spread across the code.
However, this is not a 100% out of the box solution for the port, because of the following limitations :
Feature level in ANGLE is 10 I think, while WP8 requires to target Feature 9.1. I think this should be not too much complicated to change however, and should still provide features to comply with OpenGL ES 2.0 specs.
ANGLE is making use of D3DCOMPILE for runtime compilation of shaders (dynamically translating GLSL shaders to HLSL). So we would have to make static shaders and compile them at compile-time instead. I have seen this is what is done on Cocos2D-X wp8_v2 branch, so it should be okay.
ANGLE needs to be modified to take care of C++/CX implementation to target WinRT runtime.
While this might look a big job, I think it would be a smart, clean and efficient way to merge WP8 ports into master/develop branch.
I am looking for core developers (and other developers too !) feedback on it.