Cinnamon is currently offered to users of Fedora 18, but it's not the default. If it ultimately gets adopted as such, the shift to Cinnamon will be particularly interesting given the resurgence in popularity we've seen for classic Linux desktops in recent months.
Even as GNOME 3, Ubuntu's Unity, and Windows 8's Modern UI embrace the mobile paradigm in their look and feel, there's been a seemingly endless parade of traditionally minded offerings emerging in response, including not just Cinnamon but also MATE, SolusOS and its new Consort desktop, Fuduntu, GNOME Classic, and more.
It still has yet to be decided, of course. But if Fedora goes with Cinnamon as its default desktop environment, that will surely be another pretty strong vote against the use of the mobile paradigm on the still-not-dead PC desktop.