Would be pretty useful, as far as I know there is no way to change /etc/{subuid,subgid} in the system configuration without manually editing.

Well I had to make one :) it is being tracked on https://issues.guix.gnu.org/72337 . You can define subuid and subgid ranges like so:

(use-modules (gnu system shadow)      ;for 'subids-service-type'
                         (gnu system accounts))   ;for 'subid-range'

(operating-system
  (services
    (list
      (simple-service 'alice-bob-subids
                      subids-service-type
                      (subids-extension
                        (subgids
                         (list
                          (subid-range (name "alice"))))
                        (subuids
                         (list
                          (subid-range (name "alice"))
                          (subid-range (name "bob")
                                       (start 100700)))))))))

which would yield

# cat /etc/subgid
root:100000:65536
alice:165536:65536


# cat /etc/subuid
root:100000:700
bob:100700:65536
alice:166236:65536

Another annoyance with podman on guix is making / a shared mount doesn’t work so changes in mounts aren’t propagated.

I think I solved that by using a Shepherd service run on boot calling mount --make-shared / . I didn't do extensive testing of mounts but I'm currently using this on my systems as it's set up in my personal channel. By adding the following to my own system config

(use-modules (small-guix system accounts)
                         (small-guix services containers))

(service iptables-service-type)
(service rootless-podman-service-type
               (rootless-podman-configuration
                (subgids
                 (list (subid-range (name "alice"))))
                (subuids
                 (list (subid-range (name "alice"))))))

I'm able to run the following rootless Podman hello world

$ podman run -it --rm docker.io/alpine cat /etc/*release*
NAME="Alpine Linux"
ID=alpine
VERSION_ID=3.20.2
PRETTY_NAME="Alpine Linux v3.20"
HOME_URL="https://alpinelinux.org/"
BUG_REPORT_URL="https://gitlab.alpinelinux.org/alpine/aports/-/issues"

and with guix shell podman-compose I'm able to run this Podman compose hello world:

$ mkdir data
$ echo hello world > data/index.html
$ podman compose up -d

...

exit code: 0
$ curl localhost:8080
hello world

So some kind of mount appears to work. Thank you for your feedback and feel free to try the service from my own channel if you are interested in providing more or in trying rootless podman on the Guix System.

For my non-guix (and foreign) systems I've switched to Podman, but for Guix System I've fallen back to Docker as I haven't gotten up the time and courage to deviate too far from the documented/mainline approach so that I can use Podman; hopefully they'll get some updates to address's it

I feel kind of bad about this but I refuse to join Guix IRC. I use mailing list out of frustration but these communication channels are the proof that Guix is not only a nice, useful and open project but it has born a project for fossbro babyboomers. It is a golden walled garden for themselves , I don't feel ok in that space.

EDIT: I've answered a little emotionally. Let me clarify, I believe most Guix maintainers act of of good will and they want to find some communication platform which is inclusive for everyone (since it is clear also to rocks that IRC is good only for someone born before 1990, so it is good for people aged >= 35) . Some of the maintainers, and some most noisy members of the community make it so bad for everyone else but themselves that, having so much explicit and soft power, the discussion about moving away from communication protocols older than CDs was closed stating "everything is perfect as it is, we reach exactly the right set of people, we do not care of increasing the userbase or making the community more inclusive".