AMD has been a supporter of coreboot for the past several years. AMD has also made made BIOS register docs available and many comments are allowed in the coreboot source.
The problem with Intel is that even though Google has provided coreboot source for a few Intel chipsets the source contains no comments for what those magic settings are for and what the other settings in those registers will do. Intel also makes it very difficult for anyone but a chosen few to obtain BIOS register docs. If this situation were to change then I'd see less problems with designing Intel mainboards for this project.
We could make an exact copy of the Google laptop boards and use the coreboot source but then why not just buy a Chromebook?