These files have existed for a little while now but I never got the official OK to distribute them. However, one of my readers (Marius Steffen) was given two Dropbox links via LEGO Customer Support to these specific files. That must mean that the documentation is no longer under NDA and so I now feel no reason not share them with the rest of the world.
The Build Your Own Block zip file contains documentation and a development environment like the standard graphical IDE but with some extra features. Using these docs and the special development IDE, you should be able to create your own blocks for the normal LEGO MINDSTORMS EV3 programming environments (retail and education). I’ve put it up on a MEGA file repo, and you can download it here: [LINK]. It’s around 300MB. Please note that unless you are planning to build your own blocks, this build will not be very useful to you. I also have NOT used this, so if you’re having trouble with it, I am not sure I’ll be able to help you, other than the usual “Did you try turning it off and on again?”.
The other zip file contains all the hardware schematics of the brick, sensors and motors, as well as detailed descriptions of protocols and mechanisms for the firmware. This one also lives on my MEGA drive and can be downloaded here: [LINK]. This is only a small zip file of 2MB.
The original Dropbox links can be found here: [LINK] and [LINK]. I scanned both files with Avast! and found no threats. That’s not to say that there aren’t any, just that I didn’t find them. Use at your own risk, and all that other legal jargon. Hopefully LEGO will release these through their website soon. In the mean time, have at them. To be clear, do not contact LEGO for support about the contents of these files.
Update 26 Oct 2014: the Dropbox links are dead, just use the ones on the MEGA file repo.
Thank you Marius for the heads up!