It might be, but last time I tried Qt on mobile I ended up redoing the app in Java, C++/CX with XAML with C++ for the common code.
The effort for doing from scratch native widgets in QML was greater than the approach I took, specially because Qt didn't provide wrappers for the APIs I cared about.
QML is designed with mobile in mind. For heavy desktop UI, Qt Quick Components, kinda fills the need.
Qt Quick 3 would be unwarranted, but a lot of maturation needs to happen.