I agree that a documentary would be cool, but I'd be hesitant to say that it would need to be produced under the guise of a network or other professional organization. If anything, I'd love to see a glued together collection of videos from the founders, pg, and the rest of the team (sort of like pg's post not too long ago of pictures of the early days of YC). It doesn't have to be produced to be entertaining and the story wouldn't need to be written (it would simply be the YC companies going through the experience).