As outlined in my earlier article covering XDG-Shell for Wayland, "The premise of xdg_shell is more sharing of Wayland-related code and concepts amongst desktop environment developers with those implementing their own compositors for their desktop user-interfaces. Xdg-shell in relation to Wayland has been compared in nature to EWMH (Extended Window Manager Hints) to X11."
With this commit, the first of the XDG-Shell protocol work is now in place but the protocol isn't yet stable and will be refined upon further feedback from desktop developers targeting Wayland support.
See the earlier article for more details on XDG-Shell. This work will be part of the Wayland/Weston 1.4.0 release.