Kristian has two X Servers running within Wayland and at the same time still having Wayland's terminal open. This is done using just Wayland and not Xnest, Xephpyr, or other techniques. The contained X Servers aren't limited either but they are still capable of Direct Rendering Infrastructure 2, GLX, X-Video, and UXA acceleration (the EXA-based system that's been GEM-ified by Intel).
Input events are passed to the X Server from Wayland instead of using evdev, but this side-by-side X Server action currently doesn't support keyboard inputs.
Congratulations to Kristian Høgsberg in accomplishing this nice little feat. Wayland is coming along quite quickly and nicely to say the least. Read more about it on his blog.