I use qemu for a lot of coreboot work. I really depend on qemu for many things I do, not just coreboot related. The qemu target in coreboot has been very heavily used by us to test out new ideas.
That said, I don't see a compelling need to augment seabios with coreboot on qemu *in the standard distribution*. If seabios gets the job done, and gets OSes booted, I think that's sufficient. I don't see a need to complicate anyone's life with something that is, after all, a sideshow for qemu users.
Conversely, I don't see the need to add the huge pile of stuff that comes with UEFI/OVMF/whatever to qemu either. One might argue that having any BIOS callbacks in the OS is a huge mistake, and certainly I've learned in practice that this argument is true.
thanks
ron