Wayland support still seems to be far off. There is a proposal, and they're talking about putting Wayland support in. But there has been little code written. The biggest issues seem to be about nVidia support.
As for nVidia, they have chosen to use the GLX extension, while Wayland uses EGL. Until nVidia switches to EGL, Wayland support is going to be far off.
As for performance gains, I can't see any (then again, I only use Linux, and I don't know much about Wayland).