At some point, the KDE4-era KDM is going to end up unmaintained. The preferred display or login manager for KDE Plasma 5 is SDDM, which is Qt-based, and QML-themeable. In Area51, the unofficial KDE-on-FreeBSD ports repository, we've been working on Plasma 5 and modern KDE Applications for quite some time. One of the parts of that is, naturally, SDDM.
There's x11/sddm in the plasma5/ branch right now, with a half-dozen code patches which I'll have to look in to for upstreaming. I decided to try building it against current official ports -- that is, current Qt5 on FreeBSD -- and using it to log in to my daily FreeBSD workstation. One that runs KDE4. That is immediately a good test, I think, of support for not-the-obvious-X11-environment for SDDM.
So the good news: it compiles, installs, and runs. We've added a few tweaks, and still need to figure out which packages should be responsible for adding .desktop files for each environment. SDDM now installs an xinitrc.desktop, for the most-basic case. Switching kdm_enable to sddm_enable in rc.conf is all you need.
The bad: some things aren't there yet, like shutdown support. And, at least with my nVidia card, fonts can vanish from the login screen after switching vt's.
The ugly: we really need to spend an hour or two on doing some branding material for SDDM / Plasma 5 / KDE Applications on FreeBSD. Basically slapping Beastie on everything. Graham has created some graphics bits, so we've got something, just not packaged nicely yet.
Speaking of the Good, the Bad, and the Ugly, I re-watched it recently, but now with the added interest of figuring out where in Tabernas or Rodalquilar it was; turns out the beach past the airport is also part of the desert scenes. And SDDM can soon be part of the FreeBSD scene.