My apologies: I was just confused about the syntax of bind entries in /etc/fstab.
"bind" goes in the options field (no ",defaults" needed), whereas "none" goes in the type field. I tried it this way and mount works just fine on Guix as well as on NixOS and Debian and other Linux variants; and with my incorrect syntax (with "bind" in the type field) it fails on all of them. Now, whereas the guix manual does need clarification about "bind-mount", I see that there is a recipe in the cookbook that specifically explains how to declare bind entries in Guix.
