They'll make it in, Fedora 18 will get it too. Fedora does 1 big DE update per release
I don't really think 18 will get it. I've never seen them do major updates on software after a Fedora release.
I'm always open to be proved wrong though. It doesn't really matter to me because I always have my Xfce self-compiled (to stay up to date).
Why? I don't see any reason for switching. GTK3 is a slower than GTK2, which I find totally unacceptable. New toolkit releases should tend to be faster like it's with Qt 4 -> Qt 5.
So why switching?
Oh, I didn't know it was slower.
My understanding is GTK3 is much more modern with CSS-like support.
Then it would be nice if everything migrated to GTK3 so we can drop GTK2 instead of run GTK3 and GTK2 side by side.
Hm, the move to Gtk3 is sad news… It means crappy themes and broken scrollbars .
Also Thunar 1.4 is better than 1.6. The new shortcuts pane wastes vertical space and the reload button is in the wrong place (à la Firefox).