I'm making some progress. The culprit for the grub error was: (let ((inputs - '#$(append (list qemu parted grub e2fsprogs) + '#$(append (list qemu parted e2fsprogs)
There is more work involved than I thought. Support for cross-compiling stuff like /gnu/store/2z7jlxzhyll5i9imiizsyvfygsa88k55-activate-service.drv needs to work somehow. That gets us at least guix system build working.
