That's not a "system daemon". Let's break it down:
- init: start/stop services
- inet: start/stop services
- cron: start jobs on a schedule
- atd: start jobs on a schedule
- watchdogd: restart services
Notice the commonality? launchd launches services, possibly on a schedule.
> I mean where do you think systemd got the idea from? :)
systemd is monolithic and system-invasive in ways that launchd never could be, or that anyone wants it to be. Just take a look at the systemd feature list[1]: Quota handling, swap handling, encrypted disk handling, kernel module loading, graphical UI, syslog replacement, console/keyboard configuration, X11 integration, fsck handling, serial console handling, and more!
Systemd is a crazy kitchen sink of a project. It's no wonder that it's non-portable, and I can't imagine trying to evolve the components of a system that came to rely on it. The minute you want to change how an OS subsystem works (eg, such as the automounter), you'll have to dig into the non-portable/non-abstracted systemd code.