systemd-sysupdate already exists. systemd won't run the software repository of course, but with systemd-sysupdate together with some overlay mounts you can get

systemd-sysupdate already exists. systemd won't run the software repository of course, but with systemd-sysupdate together with some overlay mounts you can get Steam Deck-like ease of use system updates. For software management in R/W environments, there's the podman + systemd combo that'll let you run containers like normal systemd services.