This new patch-set supports force and filled modes for handling if the requested surface size of the Wayland Display Server doesn't match the output size. The force mode finds a matched mode and set's the screen's mode while the fill mode will apply black borders to the surface in order to match the screen's mode. I.e. for gaming or other select applications if you're after running them full-screen.
This latest patch-set to Wayland can be found on the Wayland mailing list.