There's already been many Phoronix articles in the past three months about the Wayland/Weston 1.4 changes and new features, including an outright listing of the new features to Wayland 1.4. However, again, I will list some of my favorite features to this quarterly Wayland update.
Wayland itself wasn't too exciting for the 1.4 release as most of the major work is done and it's stabilizing quite nicely while the Weston reference compositor is what's continually being refined. However, one really nice addition is the sub-surface protocol.
Weston 1.4 meanwhile has logind support, improved output handling, improved touch-screen support, nested compositor buffer pass-through, and crop and scale protocol support (not yet in upstream Wayland protocol).
Wayland/Weston 1.4 is coming at a nice time with there being many other Wayland-related projects releasing in the months ahead including GNOME 3.12 with its superior Wayland support and Enlightenment E19 with full Wayland support. There's also new small Wayland projects sprouting each day like SWC that was talked about yesterday, the Qt5+Wayland Hawaii desktop, etc.
The official Wayland/Weston 1.4 release announcement can be found on the Wayland developers' list.