Wayland and X11 are protocols, they are essentially just documentation. You need an implementation to be able to actually run programs on it, called a compositor. People tend to think of X11 as a single software because historically Xorg became dominant as the main implementation of the specification, so most of us have only ever used Xorg (but Xorg is not the only implementation of X11, there are many others). Wayland, as a newer protocol, hasn't undergone such consolidation yet, there are many competing compositors implementing the protocol in their own way. GNOME has one such compositor, and KDE has their own, and there are many others. So it's not about "Desktop Environments" all running over the same compositor, as it was on Linux in the Xorg days. Instead, the Wayland features you get are the ones your choice of compositor has already implemented, and can vary between different compositors.