According to the GNOME Wiki, the intention had been to default to a hybrid Wayland session in the next major release, version 3.12, due this March.
But, announcing a change in those plans in a mailing list post, GNOME developer Matthias Clasen explained:
“GNOME 3.12 / Wayland will still be [a] 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 destabilising the X support at this point, so we will defer the merging of the mutter-wayland branch until after 3.12.”
Whilst basic functionality of GNOME Shell as a Wayland compositor does, at present, work – with most of GNOME’s core apps fully supported – there are gaps remaining that GNOME developers are hoping to plug before the March 26 release of 3.12.
Items on the to-do list include enabling a Wayland session to be launched from the GNOME Display Manager (“login screen” to you and I); supporting keyboard shortcuts, and supporting the libinput library.
Like the last major release, Wayland will be included as an ‘experimental preview’. But this won’t, however, be able to handle Wacom tablet input; and will lack support for mouse and trackpad device configuration, drag and drop and clipboard features, and status icons.
Like Canonical’s Mir display server, Wayland is not currently supported by proprietary drivers, but is supported by a number of open-source drivers, including Mesa. It also supports an X server compatibility layer for running legacy applications.