Finding a KDM substitution for future Fedora KDE releases
KDM is obsolete (still bears the XDM heritage) and nearly unmaintainable.
KDM is buggy.
KDM won't survive switch to KDE Plasma Workspaces 2.
KDM is written in C despite object orientation of most parts of its design.
KDM doesn't support QML/QtQuick themes.
We can get rid of KDM entirely, there's a cmake switch for that in kde-workspace: 
What can we do now
Further maintenance of KDM
KDM doesn't have any really active maintainer as of July 2013.
Many bugfixes (not even mentioning features) would require a major structure change and rewrites in many parts of the project.
Switch to SDDM
New young project with decreasing activity of the main developer.
Those of you who talked to me about it already know I'm convinced SDDM is the way to go. When time allows, I'm trying to add XDMCP support to it and have promised to write and test logind-style multi-seat, too. --mbriza
- pure C++ and Qt (already prepared for Qt5)
- nice, clean and logical design
- Many missing features (most notable: XDMCP, VNC)
- Decreasing developer activity (which was really huge initially, reduced pace was quite expectable)
Switch to LightDM
The main DM of Ubuntu is developed by Robert Ancell and is covered by the Canonical CLA.
As Ubuntu will be switching to Mir (in 13.10 as far as I remember), we'll see how they'll handle using it instead of X as a backend. If it'll be possible to easily switch those backends, there would be a ground prepared to add a Wayland one.
- David Edmundson's Qt bindings for QML/QtQuick greeters
- Provides API for creating greeters in virtually any form
- Actively maintained and developed
- Written in C using GLIB
- To me, it really doesn't seem "light" enough, starts slower than KDM and takes more memory, too.
What needs to be done:
- Add the conditional KDM inclusion parameter to
kde-settingsnot to ship KDM settings
- http://www.freedesktop.org/wiki/Software/LightDM official web
- http://www.sharpley.org.uk/node contains release info and interesting discussions (unfortunately there are no tags to filter the articles)
- http://lists.kde.org/?l=kde-core-devel&m=130799230315640 a quite lenghty thread comparing KDM to LightDM in the KDE-core-devel mailing list
- http://mjg59.livejournal.com/136274.html An article describing why it maybe is not such a good idea to switch to LightDM