I had a dream last night. I fell asleep pondering GPU rendering. In my dream, I realized that we’ve had a GPU renderer in blender all along. THE BGE :eek:. It, is capable of rendering things at a speed unparalleled by processors. All we need do is retool it. It wouldn’t be too hard, because most of the stuff is already there. Yeah, it wont support some features the actual internal renderer does, but it has seen tons of improvement recently. Now, for the question. Could this be done completely in python? It would make it even easier to improve upon. Just thought I’d get this out there.
Good dream! I would love to see more realtime rendering features. What if all the styles from freestyle where to be editable as GLSL shaders. Now that would make blender a killer realtime NPR render 
As you say it is not quite as easy as to just convert the internal render to BGE with just python. But on the long term having more GPU based rendering features will definitely help in a production where speed and approximation is more important than physical accuracy.