Comment # 3 on bug 898876 from Jon Grossart

(In reply to Stefan Dirsch from comment #2)
> Any prominent desktop, who is planning to use lighdm or sddm as default
> displaymanager? I'm not interested in adding douzens of DMs.

No DE directly uses lightdm (other than Ubuntu's Unity). However, it is
referenced in the wiki as a recommended display manager to use for testing out
Qt5 KDE.

Also, I believe KDE isn't moving kdm forward to Qt5/KF5 and is supposed to be
switching to SDDM. (Definitely for Fedora, as it's the default for F21 KDE).
The other option passed around is just using LightDM.

Frankly, those are the only two major ones not listed already.