The gtk+3.0 3.6.4-0ubuntu2 package was uploaded to the Ubuntu 13.04 "Raring Ringtail" archive on Friday, which enables the Wayland back-end. This Wayland back-end for GTK3 can be dynamically enabled at run-time via setting the GDK_BACKEND environment variable to wayland.
With GDK_BACKEND=wayland set, common GTK+ applications should now be able to launch and (at least mostly) work within a Wayland/Weston environment. You can try this by installing Wayland/Weston from the Ubuntu archive and using the weston-launch executable.
Among the applications known to work right now on Wayland that are dependent upon GTK+ include the GNOME Calculator, Baobab, File Roller, Charmap, Gwibber, Brasero, GNOME Sound Record, Gedit, and GNOME Terminal. Some GNOME packages like GNOME Sudoku, GNOME System Monitor, Nautilus, Rhythmbox, Totem, Chromium, and Firefox are not working at this point. Applications using direct X11 calls or other non-standard functionality will require additional work to be ported to a Wayland-friendly world.
Enabling the Wayland back-end for GTK+ in Ubuntu closes this Launchpad bug.