What about initrd? Most of those use busybox and it's now "recommended" to start systemd there. (Granted, I don't see why anyone would run busybox's syslog - the only component affected by this change - in an initrd.)
If you want an extremely small system, you can put everything you need into the initrd. It's not strictly an initrd then, since it's not really used for bootstrapping a larger system image.
