It turns out that Wayland won’t be enabled by default in GNOME 3.12, as the developers hoped, and it will have to be pushed back until the GNOME 3.14 launch.
The implementation of Wayland in GNOME 3.12 has been proposed a long time ago and for while everyone believed it would be ready just in time. GNOME Shell, Mutter and all the other components got support for Wayland, but there are still too many problems left.
“GNOME 3.12 / Wayland will still be preview. There are still too many unfinished tasks, and we are only a few short weeks away from hard code freeze. We don't want to risk destabilizing the X support at this point, so we will defer the merging of the mutter-wayland branch until after 3.12. And we will of course continue working on the TODO list right after 3.12, some of the gaps can probably be fixed in stable updates,” reads the announcement from Matthias Clasen.
As it stands right now, only a small part of the proposed features work, and even those are not up to full speed. For example, GNOME Shell can act as a Wayland and X11 compositor, but it provides only limited functionality. Other working features are display configuration, color management, the message tray, and the hot corners.
Even if Wayland will not be integrated as a complete solution in GNOME 3.12, that doesn't mean that the developers won't try to get more features in. By the time GNOME 3.12 will be released it’s quite possible that users will be able to launch Wayland sessions from GDM, libinput will be used as input, and the keybindings will be ready, along with the clutter apps.
A number of other problems will still be present and will have to deal with them after the launch of GNOME 3.12 like input configuration, Wacom tablets, startup notifications, dnd and clipboard support, and status icons.
This is actually not bad news and it’s a good thing that developers pushed the integration of Wayland into a future version. The last thing that people would have wanted was a buggy version of GNOME 3.12 with Wayland as default that would get a lot of flak from the community.
If you remember correctly, Canonical also pushed the integration of Mir into Ubuntu for a later date, also because they didn't managed to get everything working as it should. Sure enough, it might have worked for a lot of users, but not for everyone.
Until then, you can enjoy the latest GNOME 3.12 Beta 1 version that was released only a few days ago.