Hi Emilian,
I chatted today with Holger from reproducible.debian.net and couldn't resist doing reproducible builds ;). These patches need additonal work, but they are working when the git tree is clean. You can test coreboot reproducible when building without payload. Or a more advanced way integrate my seabios git-tree into coreboot's payload target.
coreboot needs 2 patches (one is very dirty ;) to build reproducible. http://review.coreboot.org/#/c/8611/ http://review.coreboot.org/#/c/8612/
SeaBIOS requires one patch. https://github.com/lynxis/seabios/commit/487ef74fc6cb1b1020fb25c9bb3f166602c...
Best, lynxis