Seriously, back around the turn of the century I was pretty heavily into graphics and rendering and was frustrated by all the constraints on getting access to documentation. I finally figured out a way to pin down a vendor with all the necessary NDAs and all the necessary agreements so that I could actually get 100% access to the inner workings of the GPU. As long as I read the documents onsite at the vendor's office and brought no means to make copies. And after all of that, in discussions with the vendor's counsel, their biggest fear was that as GPUs were so competitive, and so heavily protected by IP, that they did not disclose any details to people who might see something that might be protected by some patent somewhere and defending a lawsuit, which always settled before discovery because nobody wanted to actually share their documents! It was insane.
That said, I think an open GPU is an excellent idea, however while I don't think it will get built any time soon I think just publishing all the techniques and algorithms will draw out all these lawyers and we could hopefully arrive at the 'available set' of features which one can implement. I expect though that you need a Google level VP8 kind of program for this to make progress (and Google failed there if you recall)