I recall having to run gnome-settings-daemon even if I wasnt running the rest of gnome to fix some absurd issue or other. I can see systemd easily "leaking" dependencies up the stack, making my life as a "fringe"/non-gnome user harder.

The people working on it don't seem to have any aversion at all to scope creep. In fact, the politics of it all make it seem like a "land grab" and they'd in fact be happy if systemd takes over more and more responsibilities.