As someone who works for a large silicon vendor I can tell you that even with access to those industry groups the documentation still sucks!!!! I look at the amazing documentation available surrounding various software initiatives (OpenCV, machine learning, linux drivers, programming languages, etc...) with envy. It's all right there and out in the open with multiple blogs and forums and pages explaining shit. And actually I did try to learn PCIe. I gave up. 1000+ reference specs, about 3 random web pages and a half dozen marketing youtube video's. There's a reason why some guys manage to build niche careers around these HW topics!