The Win32 GDI functions have a higher level of abstraction than the DirectX api. Microsoft will probably just recode the GDI functions using DirectX, and add someway to interact with the underlying DirectX implementation. Also, their sound api might be improved. All in all sounds like a pretty good thing. I doubt this improvement will affect OpenGL, which is just a standard. Developers really have the final say on what API to use.
I think it's about time. GPU's are way faster than the GUI. And this would mean that we would not have such a distinction any more between Win32 GUI and DirectX 9.0.