All the support is now in place for the GNOME Shell to run as its own display server, support for running Wayland under gnome-session, and other prerequisites as mentioned in this GNOME.org BugZilla entry.
As covered by many Phoronix articles, the goal has been to make the Wayland support in good shape for GNOME 3.10 as an option while still supporting running the GNOME 3 desktop on an X.Org Server. There is no Mir support present in upstream GNOME.
This ongoing Wayland enablement work has not only involved alterations to the GNOME Shell but also the Mutter window manager, GTK+ tool-kit changes, and much more.
One of the first distributions expected to ship with GNOME 3.10 on Wayland as a technology preview will be Fedora 20 though the default in this next Fedora Linux release will be an X.Org Server.
Aside from today's GNOME 3.9.92 release that merges the Wayland branch, also released today for the GNOME 3.10 Release Candidate was Mutter Wayland 3.9.92. The Mutter Wayland code contains the necessary support on its side for running as a Wayland compositor without a dependence on X11 or XWayland.
Among the new Mutter Wayland changes were pointer changes, support for hardware cursors, the gnome-session support, KMS monitor configuration, minimal support for resizing and maximizing Wayland clients, pop-up menu surfaces and grabs, transient hints for Wayland clients, and much more.
The final release of GNOME 3.10 is due next week Wednesday, the 25th of September, and certainly another thing to celebrate at Phoronix@Oktoberfest besides Valve's SteamBox news.