I'll be doing similar work in next few months, my goal is to get displayfrom coreboot-like environment, and I'm not planning to use
intel's vbios,
my experience tells me vbios is not an absolute necessecity, so the BMP or MBI stuff won't be bothered either. The idea is not verified, but I think it's worth a try.
Your right. My experiance tells me Intel's vbios is not necessary also. It is possible to get the vga and any sub-chips running without the vbios, but the problem with that is Linux (or other OS's) do not play well. You have to set them up to use the Intel frame buffer instead of the the normal "intel" X driver. It's alot of work, on both the coreboot end and the Linux end...
My theory is to use a normal vbios, after coreboot initializes vga setup the i2c lines, and then program the sub-chip (tv, LVD, etc).