That still doesn't make it monolithic. It's not exactly rare for an open source project to have no API spec. If you want to replace a part you just look at the

That still doesn't make it monolithic. It's not exactly rare for an open source project to have no API spec. If you want to replace a part you just look at the code and then implement that API. If you ask me a lot of systemd is actually pretty easy to swap if you're interested, most is separated out into clean d-bus APIs.