To allow metalog to be used in a systemd controlled system, it should be able to use its socket activation mechanism. There exist two thorough documents from the systemd author describing the needed changes:
http://0pointer.de/blog/projects/socket-activation.html
http://www.freedesktop.org/wiki/Software/systemd/syslog
I'll try to provide a first patch for further discussion.
i don't use systemd, do a patch would be best