QML is amazing for desktop apps as well. The only problem with QML on mobile is that stuff just won't look native or match native themes. Not the end of the world though.
It is worse than that. Up until 5.3, the common dialogs would render like on desktop OSes, just tinier, instead of being adapted to the mobile OSes concepts.
As far as I know it is still the case. One needs to reimplement the common dialogs in QML when doing mobile development with Qt.
http://blog.qt.io/blog/2015/11/23/qt-quick-controls-re-engin...
They already have Holo, they just need Material for newer Android handsets, and those changes are going in 5.7 coming out in a few months.