(wearing my coreboot developer hat): We care about BSD. And Windows. And Solaris, Haiku, and whatever else comes our way that runs after coreboot. The amount of care varies with developers, and Linux is indeed the OS that sees the most interest.

If BSD fails with coreboot + SeaBIOS, that's a bug, and I'd love to hear about it. And I think so would the SeaBIOS developer and the QEmu people who use the same PCBIOS implementation.