This sentence is getting rather long in a tooth. Cgroups? Kdbus? udev?
Same mantra that is used over and over again turned out to be at least deceptive if not outright lie, each time it was used.
"After udev is merged into the systemd tree you can still build it for usage outside of systemd systems, and we will support these builds officially. In fact, we will be supporting this for a long time"
http://article.gmane.org/gmane.linux.hotplug.devel/17392
"...this will effectively also mean that we will not support non-systemd systems with udev anymore starting at that point. Gentoo folks, this is your wakeup call."
http://lists.freedesktop.org/archives/systemd-devel/2014-May...
So when Lennart or somebody in the systemd team claims something to be optional you can bet everything it is not or soon won't be.