I really agree with you!
Theres http://razor-qt.org/ but its developement sems to go slowly...
And its a pre-Qt5 and pre-Qml.
QML for desktop widgets and other stuff would be nice, and not that hard to implement (KDE4 has to made the whole Plasma desktop think for the widgets).
I hope Razor-Qt would pick-up Qt5 new features and make it a good desktop.