Some containers are better run with systemd as init.

This really then has a requirement on the host having oci-systemd-hook which is not present in Debian and cannot be relied on for certain cloud services.

Should we have a guideline forbidding this and mandating an entrypoint of a suitable reaper and script to run the services, or should we permit this and have a way to document a systemd capable container host as a requirement?

This seems particularly important in environments where zombie risks are high (eg php workers) and as a result for the owncloud container with mod_php the preference would be a systemd based container, but we could work around this if required.