Took a look at your mnt-reform-guix repository...
Mostly looking to borrow examples to extract the linux patches from the reform-debian-packages as a referenced git repository rather than shipping them in guix directly... looks like you do a that more-or-less. Although my guile skills may not be sufficient to fully wrap my head around it!
Also just build tested arm-trusted-firmware-rk3588 and it is really just a two-liner patch against guix upstream. No idea if it *works* yet. :)