A few weeks back GNOME developers announced that GNOME 3.8 would no longer include the fallback mode. When users roared up, developers found a way to co-exist peacefully with them - a fallback-like mode made mostly of specialized extensions. Matthias Clasen blogged today of some of the progress of what he now dubs GNOME Legacy.
First up, Clasen explains that the mechanism for adding external modes into the login screen, which will allow additional modes like Legacy to be a choice. In fact, Clasen says, " The upshot is that we now have a ‘GNOME Legacy' session appear in the session chooser in the login screen."
rest here