Martin Gräßlin, the KWin maintainer, announced the experimental KDE Wayland support on his blog. Martin has been talking about KDE Wayland support for a while now... Originally he was waiting for a stable release of Wayland to come, while 1.0 was out last year, it's not out until after Wayland 1.1 and then Canonical's Mir announcements that we're now seeing actual KDE-Wayland progress.
Martin notes on his blog, "This backend does not allow to manage Wayland clients, but uses another Wayland compositor as the rendering target. Instead of rendering to an X window, KWin renders to a Wayland surface. From an architecture point of view this means that there is a Wayland system compositor and KWin is running as a Wayland session compositor (although KWin is not yet a Wayland compositor)."
Right now there's a number of steps involved for getting an experimental KDE Plasma desktop running atop Wayland with the Weston compositor, but for those wishing to experiment, instructions are available from Martin's blog.