xfswitch-plugin hard depends on gdm. But in gentoo can be compiled without it. USE=-gdm It is good for nothing. Only for uninstall.
What version are you talking about? There are useflags to switch between gdm / lightdm / lxdm. It does not hard depend on gdm at all and works fine with the others.
>>> Installing (1 of 1) xfce-extra/xfswitch-plugin-0.0.1-r1::gentoo * checking 7 files for package collisions >>> Merging xfce-extra/xfswitch-plugin-0.0.1-r1 to / --- /usr/ --- /usr/share/ --- /usr/share/xfce4/ --- /usr/share/xfce4/panel-plugins/ >>> /usr/share/xfce4/panel-plugins/xfswitch-plugin.desktop --- /usr/share/locale/ --- /usr/share/locale/cs/ --- /usr/share/locale/cs/LC_MESSAGES/ >>> /usr/share/locale/cs/LC_MESSAGES/xfswitch-plugin.mo --- /usr/share/doc/ >>> /usr/share/doc/xfswitch-plugin-0.0.1-r1/ >>> /usr/share/doc/xfswitch-plugin-0.0.1-r1/AUTHORS >>> /usr/share/doc/xfswitch-plugin-0.0.1-r1/NEWS.bz2 >>> /usr/share/doc/xfswitch-plugin-0.0.1-r1/README.bz2 >>> /usr/share/doc/xfswitch-plugin-0.0.1-r1/ChangeLog.bz2 --- /usr/lib64/ --- /usr/lib64/xfce4/ --- /usr/lib64/xfce4/panel-plugins/ >>> /usr/lib64/xfce4/panel-plugins/xfswitch-plugin * Updating desktop mime database ... * Updating shared mime info database ... >>> xfce-extra/xfswitch-plugin-0.0.1-r1 merged. >>> Regenerating /etc/ld.so.cache...
I'm sorry, I don't understand what the problem is. can you upgrade to xfce-extra/xfswitch-plugin-0.0.1-r2 and test? that one is going to be stabilized soon.
The problem is: - you have installed and running lightdm not gdm - you want to switch user. - you installed xfce-extra/xfswitch-plugin-0.0.1-r1 [-gdm] - you cannot switch user. But ~0.0.1-r2 works fine. So remove old buggy version 0.0.1-r1, please.