Isn't Raspberry Pi also pretty much a proprietary design? Certainly the Broadcom chipset they use isn't available to the general public, nor is information about the chipset available without an NDA.
The Broadcom chip documentation is not generally available. Beyond that, you probably can't even buy the Broadcom chip.
The GPU (the bulk of the chip's compute power) is a black box with a binary library that works with some versions of Linux for the time being but will eventually be abandoned by whoever is wrote it. That is just the current state of the world for embedded GPUs.
But looking outward…
The Raspberry Pi Foundation commits to documenting the exposed hardware of the SoC in their FAQ. (Think GPIOs, analogs, serials, etc).
I got the impression that the Raspberry Pi Foundation was thinking about how to license the design, perhaps a CC, but I don't see that they have made a decision. It is in many ways it is moot. They could give you the Gerber files, but you wouldn't be able to get a BCM2835.
