It shouldn't be a surprise that Canonical has been moving the Ubuntu desktop (namely, Unity) in the direction of Qt/QML over GTK. The Unity phone/tablet interface is using Qt as is other components and for the next major iteration of Unity they're seeking for it to all be written in Qt/QML.
Aside from announcing the Mir Display Server
today, Oliver Ries of Canonical also laid out more "Unity Next" details on the mailing list
and Ubuntu Wiki
about taking Unity to the next level.
After the Ubuntu Touch efforts, Unity is being moved to being a Qt/QML-based implementation with embracing Qt as "a community backed technology for our offerings." Unity will be transitioned from a Nux-based implementation with GTK and Compiz to now running on Qt/QML technologies.
Of course, it's a bit funny considering that the former "Unity 2D" desktop was written in Qt. Canonical dropped the Qt-based Unity 2D
last year in favor of pushing the Unity desktop that mandated Compiz. Well, now with Qt 5 around, they've flip-flopped and see Qt as the future for their desktop across all form-factors. "Fast forward 9 months, we have learned that our concerns have not been justified, Qt 5 has come out nicely and we have full confidence in using it as one core technology in our offerings."