Well it turned out EggSmClient is not _it_, the old session support in gui4 worked well for us, but it would be nice if we could turn this in a GObject api, so it provides what we need and (if possible) also a replacement for ExoXsessionClient (see bug #5671), so in the future we have 1 session api in Xfce. We should also keep in mind Gtk+ is working on this, but if we have something that works well in 4ui, I hardly care about Gtk since those guys have (at this moment) no clue what they are going to do with it. So... let design a (minimal, we can always add later) session api for 4ui.
I'm working on this... I'll check it in when it's ready.
Checked in i guess?