As I understand, Wayland has come pretty far.
What remains is improvements to the Wayland backend for GTK and Qt, and also XWayland.
GTK's Wayland backend is probably getting in pretty good shape for GTK 3.8.
XWayland is a bit unstable and needs work.
Many applications needs to be ported from GTK2 to GTK3 and from Qt4 to Qt5.
Many applications needs to stop using X11 calls and not rely on Xlib.