When Wayland started out in 2008 it was very difficult to build and run this lightweight, next-generation display server. Wayland leverages the very latest Linux graphics technologies and at that time all of Wayland's dependencies had to be patched or built from branched sources and Wayland even had its own EGL implementation at the time (Eagle) rather than Mesa and overall it was just a high barrier to entry. Wayland at that time also worked with only the open-source Intel driver, while now it can work with most any KMS / GEM / Mesa driver. It was not until recently that it became possible to build Wayland from mainline components beginning to ship in new Linux distributions, thereby making it much easier to experiment with the open-source display server. Now it's to a point where you can just run a simple script and be up and running with a Wayland Display Server in just minutes.
The demo looks very interesting...does Wayland actually improve display performance vs the standard Xorg server?
If Wayland takes off, wonder if nVidia and AMD/ATI will consider providing support for Wayland in their proprietary display drivers?
What about having to recode applications that make calls to the server, if Wayland's API will be different than Xorg
Fortunately for maybe 98% of apps the transition should be pretty seamless, once toolkits get proper support for wayland. There may (and will) be problems with things like display and window managers, which directly interface with XLib. Also I think (but I'm not sure) some older games use XLib to change the resolution. Ah, and SDL would probably need to be ported too.