When I said "given serious consideration to how much work it would require to duplicate those features on another platform", that allows for the possibility of providing the same features systemd does without using the platform features it currently requirs. Even allowing for that, I think my comment still stands: doing so would require a prohibitive amount of work.
You don't have to use cgroups; you do have to support the features systemd currently uses cgroups to support, such as supporting daemons that fork or double-fork or have child processes, while still respawning daemons that exit or crash. Upstart handles that "portably" by ptracing daemons that fork and capturing the relevant PIDs; that approach requires a great deal more code and work than using cgroups, because that approach doesn't rely on a platform feature specifically designed to support it.
Now repeat that exercise for the hundreds of systemd features supported by Linux platform features.