Seems you're just confusing things. Why do you suggest systemd is monolitic. What is the problem actually? There are various independant parts. E.g. the logind

Seems you're just confusing things. Why do you suggest systemd is monolitic. What is the problem actually? There are various independant parts. E.g. the logind bit is now used by Canonical on upstart. Seems your issue is some theoretical problem while in practice systemd is just not monolithic.