The parts that aren't already replaced are heavily patched and can't really be used by a default install.
Re:GNOME (et al): Rotting In Threes
by crowleysimon on Thursday November 08, 2012 @09:36AM
(#4757910)
I wouldn't say GTK+ is next, unity2D is discontinued and Ubuntu One is only made in QT because they use the same client for windows and mac.
The replacing of Gnome has already begun. They replaced Gnome Shell with Unity and GDM with LightDM. They're using Qt more often now as well (I believe Ubuntu One is Qt and I know that Unity2D is too), so it seems that perhaps GTK+ will be next.