The open source part of Tiano doesn't make a firmware on x86. It's missing _all_ early hardware init because Intel considers that secret.

Combining coreboot and Tianocore can build an open source x86 UEFI. But unless you need the network boot feature, UEFI is a waste of time and space.

And I also forgot to mention that OEMs don't typically ship Win8 machines booting with legacy BIOS. But they are not likely to adopt coreboot anyway.

You can boot Windows with UEFI, and it is easier to implement than legacy BIOS (which requires a lot of reverse engineering).

legacy BIOS: see www.seabios.org, written in C.

It's good enough for KVM (that Linux virtualization technology), which boots Windows all the time.

Many coreboot installs(including those on x86 chromebooks) have SeaBIOS included. you just press C-l at boot and it drops you into the standard PC BIOS. If you've gone through and removed the warranty-voiding screw(which is not warranty-voiding in europe) you can enable it by default(and also just load your kernel directly as a payload, which I think is a better idea).

There is also talk, and perhaps actual implementation, of TianoCore running on top of coreboot.

SeaBIOS is also used by VirtualBox, and probably Xen as well.

Which doesn't matter since both seabios and tianocore already exist.

But seabios is much, much easier to integrate because it has fewer moving parts