Earlier quoted context omitted.
Mac OS's architecture is totally unlike systemd. Areas of responsibility are implemented by standalone mechanisms that compose to create the larger integrated system and can: 1) Run in isolation from their upstream dependents. 2) Be replaced individually.
Lol no. On many levels. MacOS does implement separate daemons, but they're all very tightly integrated, communicating over a common protocol. The core components hardly run in isolation, nor are they interchangeable. You don't, for example, just replace launchd with some other init system. You don't just say "hey, screw Aqua I want to use something else." (You can run other WMs through X11, but only on top of Aqua) D…
What common protocol? Mac OS X doesn't have dbus. It recently acquired XPC, but XPC is NOT a system bus -- it's simply an IPC library. It's neither required, nor universally used, nor is it terminally glued to the remainder of the OS.
> You don't, for example, just replace launchd with some other init system.
You don't? Says who? All launchd does is serve as an inetd/cron-esque daemon. The system daemons themselves continue to vend standard sockets and mach ports, and launchd itself does not pervade their externally vended interface.
> You don't just say "hey, screw Aqua I want to use something else."
Actually, you can. The display stack is driven by IOKit; XDarwin can run directly atop said stack.
Likewise, none of the "Mac-like" features that you want -- for example, automatic network configuration -- rely on any sort of centralized entity that pervades all daemons. There's a seperate system -- SystemConfiguration -- that provides that functionality, abstracted through a set of well-defined APIs and modular and distinct from the remainder of the system.
> * It's a collection of daemons running that communicate over a common protocol.*
Hence it's really rather monolithic, because to play in the systemd universe, everything has to conform to systemd's tightly coupled design.