In its defence, the portability problems are largely because the linux kernel has awesome features (ie, cgroups) and other kernels don't -- I think it's better for the world if we encourage the other OSes to add cgroups-like APIs to their kernels rather than hold linux back
Why turn things around? Systemd makes Linux specific features available. Nobody ever complained about FreeBSD having jails. Yet there are complaints that Linux has Linux-only features.
So by using your FreeBSD jail example: Because there aren't any complaints regarding jails, systemd should not be complained about.
on the other hand wouldn't that imply that people can't innovate with other solutions in the same space (groups') because they are locked into it by the init system depending on it?