Oh, ok, so getting X.org running under Wayland was easier than expected. Or I guess, it was as easy as expected, which is usually never the case.
What's running here are two X.org servers, side by side under Wayland. It's not Xnest or Xephyr, it's the full X server with DRI2, GLX, Xv and UXA acceleration. The only difference is that the server passes its front buffer handle to Wayland instead of passing it to kernel modesetting and it receives input events from Wayland instead of evdev. And Whenever the Intel DDX driver flushes its batchbuffer it now also sends a damage event to Wayland.
There's some weird transparency going on, and the reason is that the X servers window pixmap doesn't have a well-defined alpha channel. Which doesn't matter when the hardware is scanning it out to a display, but in this setup it causes some unintended transparency.
The Wayland server transforms the input events to the surface coordinate system of the client surfaces, which means that the X servers are fully functional, and you can click the icons and move the tiny windows around. It's all very cute. Keyboard input isn't working yet, but it shouldn't be too hard, since I think can get away with just passing the scan codes to the X server.