Nice to see you here, @jackhill! Indeed I am also confident that it should be possible to make most of the functionality of the Reform machine available in a fully free distribution - after all, this is the point of the endeavour, free hardware for running free software! And clearly the more is upstreamed to the kernel and uboot, the easier it will be.
At least with booting from an SD card, we can be sure to not break anything definitely ;-). I would be happy to get a Guix system running in any way, then one could still look at more involved setups.