Comment 7 for bug 1431609

Michael, Andreas, Colin, Martin; I am sorry, my intention was not to spam random people, it was to notify the people known to possess the relevant skill set required for this task.

Tim, yes Vivid does have the systemd package and the gnome-shell package, as well as the gnome-session-wayland package.
However to start a Wayland session of GNOME, you either have to run 'gnome-session --session-gnome-wayland' from the command line, or manually start GDM and select GNOME on Wayland as the desire GDM session.
There is no systemd session to start GNOME Shell at boot, and you have to go via a GDM with a X11 backend.
So there is still a hard dependency on X.Org Server.