Well, most of the users are developing games which are obviously played by users of windows. I don't think porting to OpenGL is worth the effort. The times when games supported DirectX, OpenGL and DirectX are gone. I personally would prefer conitec to put their effort in realsising the forecast features, especially the 2D improvements like speeding up the rendering of true type fonts etc.

Additionally users of Linux can use DirectX distributions for Linux like e.g. WineX.