In xfdesktop the file doc/README.kiosk indicates that the kioskrc location is $sysconfdir/xfce4/kiosk/kioskrc which turns out to be correct although not in line with the new "xdg" location. The HTML documentation for xfce4-panel suggests {sysconfdir}/xdg/xfce4/kioskrc Looking in the libxfce4util/libxfce4util/Makefile gives the authorative answer -DKIOSKDIR=\"$(sysconfdir)/xfce4/kiosk\"
Fixed, uses $(sysconfdir)/xdg/xfce4/kiosk/ now.
Ok, panel documentation was updated as well. In BETA2 all should be well.