It's not really a case of "allowing" Android apps. It would take a monumental engineering effort.
Windows runs OpenGL just fine (look at anything iD Software puts out). It doesn't run Google's custom Java VM, it doesn't offer AOSP APIs and it doesn't offer Google Play Services. THOSE are the obstacles to running Android apps on Windows, not your obsession with OpenGL vs DirectX.
In fact, if Windows Phone ever got decent market share they'd be in a great place for gaming, if they made Xbox -> WP ports easy.