I see this kind of thing mentioned a lot which really disappoints me because systemd is not as monolithic as people seem to think it is. systemd (the init system) is a relatively small component with a modest set of dependencies. systemd (the umbrella project) includes a number of other projects which are separate and many of them aren't even required and are easy to replace with something else if it's needed.
If you're a programmer I highly recommend taking a quick browser through the systemd source code, it doesn't take long to see that it isn't really monolithic at all and is in fact a combination of individual tools which are combined to accomplish things. Just because they're all under the systemd umbrella and all in the same repository does not mean it's all one binary and that parts can't be swapped out.
Even if systemd is at the very high standard of kernel reliability, it would be better design to break out the monolithic parts where possible. The kernel is the way it is because it needs to be, not because it's a preferable way of writing code.