The xfce4-session 4.13.0 package was released today and it's a significant step forward for Xfce's session manager.
Changes include the Xfce session manager being ported to GTK3, session management for clients being done using the GTK application D-Bus interface, and it's been ported to using GDBus. The xfce4-session update also adds a "switch user" button to the logout dialog, UPower dependency has been removed, and various other changes.
More details on the xfce4-session 4.13 release can be found via this Git commit. Great to see the transition of Xfce to GTK3 (and GDBus) still continuing to progress albeit rather slowly. Hopefully it won't be too much longer before seeing Xfce 4.14.