The tool-kits and other components that will be needed for Wayland to be a viable desktop display server are only beginning to stabilize and the open-source graphics drivers from Intel / AMD / NVIDIA (Nouveau) are beginning to function properly. However, there's still the very popular proprietary drivers from AMD and NVIDIA that are not compatible with Wayland due to the lack of kernel mode-setting (KMS) and Graphics Execution Manager (GEM) buffer support along with other open-source drivers (i.e. the missing VIA code and many others) that also lack these attributes.
When asking Mark about this, he responded to me, "The transition will take time, we will not cut over the whole of Ubuntu by default immediately. We'll work with vendors to support the needed capabilities. This is a strong signal to them to start work on lining up their own efforts to make it a good transition."
Well, at least as of right now, NVIDIA is claiming they will not support Wayland. NVIDIA's Aaron Plattner has publicly stated, "We have no plans to support Wayland." There is a discussion about this NVIDIA comment regarding Wayland already being talked about on our forums.
In order for NVIDIA to support Wayland by their proprietary driver in its current form, they would need to implement kernel mode-setting support and also some interface for GEM to their existing memory manager (they wouldn't gut their existing memory manager for GEM/TTM since it would be a major regression in terms of features/capabilities and performance), among other work. AMD also has no plans to support Wayland at this time by their proprietary Catalyst Linux driver.
We will see if things change once Wayland matures and there are user-land applications actually running well on this lightweight display server, but for now you will need to be using the latest open-source Radeon / Intel / Nouveau drivers if you wish to toy around with Wayland.