As per Fedora 20 change tracked in Bug 998542 (SDDM as the default KDE display manager instead of KDM), we need to have the display manager preset to autologin the liveuser in the live images of the KDE spin. I'm attaching a patch to do so, for spin-kickstarts package.
Created attachment 792853 [details] Patch to set SDDM to autologin liveuser on the KDE live image
Committed in fedorahosted: master: https://git.fedorahosted.org/cgit/spin-kickstarts.git/commit/?id=e1715dc151bf20011da255d4db87d07f735586ff f20: https://git.fedorahosted.org/cgit/spin-kickstarts.git/commit/?h=f20&id=f573b2905bfda13ccb34fdf9cf4b25cf0466cef2 Composes are done directly from the git repository on fedorahosted, so this should be sufficient. But the change will also be included in the next spin-kickstarts release.