KDE really, really needs logind - it can't really use ConsoleKit any more. Same with SDDM, though I think the CK2 backend is still writhing in agony somewhere in its codebase.

And KDE's touchpad integration relies on libinput, which relies on udevd. I think libinput might work with mdev if you really try hard enough?

I am not aware of KDE having dependencies on any other bits of systemd, at least Plasma 5 LTS doesn't.