It is also flashed with HEADs and I have a secret on a smartcard (usb stick) that I can use to sign my boot partition.
On the boot partition there will be a minimal system that lets me decrypt my hard drive and boot into my desired guix system generation. The boot partition is signed so it should never change (especially not every time you update your system configuration).
Guix allows you to bootstrap from a minimal seed so once I finish making the software I need for the bootstep I will set this up on that laptop by bootstrapping guix.
For me it's all about trying to go closer to the foundation a la precursor; rather than a theatre like qubes where the complexity is just too much.
In the not-as-distant-as-it-may-seem future I will probably try genode on a pinephone or a laptop and maybe it will be useable and robust..