I think it would be plausible to get most of the kernel patches merged into guix master; that’s what I worked on in the wip-mnt-reform branch.
Das U-Boot will have to come from somewhere else, either a channel specifically for the mnt/reform or maybe non-guix … or just manually installed from the binaries provided by the MNT folks.
If you want a kernel with HDMI and whatnot, you would probably have to use a non-guix or similar channel.