seabios is the project you're looking for, and yes now I want to go see if it supports being booted from GRUB:)
EDIT: The answer is yes and it's been done: https://g00se.org/2016/11/seabios-on-libreboot.html (granted, that's booting directly from coreboot to GRUB, but it should be the same booting UEFI to GRUB AFAIK)
Alternatively, we can be happy that some legacy systems actually die when they're no longer useful. My general attitude toward retro-computing is that the good old days weren't actually that good. I, for one, don't care if the original meaning of "PC" passes into irrelevance.
As if BIOS is any more open than UEFI is. At least UEFI had an open reference implementation since the beginning. BIOS had to be reverse engineered from IBM's implementation AFAIR.
Besides, two wrongs don't make one right. BIOS was a clutch from the beginning (it was probably appropriate for the time tho) and we should strive for better. We should keep functional systems working of course (e-waste is a real problem), but we shouldn't keep using it for the new stuff because we see the past with rose tinted glasses.
Rather than push for the past we should push for the future, for having all boards ship Coreboot and have that support upstream instead. That's how you achieve openness, not by sticking to _proprietary blobs_ of an outdated interface.
