It's sort of funny for me how the systemd attitude towards portability is quite similar to that of the OpenBSD community, whose software (OpenSSH, OpenSMTPD, OpenBGPD...) generally runs on OpenBSD only and where porting is done by a separate team, but somehow the interwebs aren't full of rants calling the OpenBSD people jerks for not caring about non-OpenBSD platforms...
OpenSSH seems to be the best known of the bunch, and even then it is loosely couples to the rest of the system.
Systemd on the other hand is rightly couples to the Linux kernel (to the point that you may have to update systemd and the Linux kernel in lockstep), and its many sub-systems are tightly coupled to the existence of systemd-pid1.
This makes systemd a whole other beast from OpenSSH.
