It looks like ros_qml is a python script that loads QML as python QT application: https://github.com/bgromov/ros_qml/bl... , so it might be possible to adapt that to run inside of an rqt plugin instead of as a standalone application.
I'm not sure what else rqt_qml is doing during the setup (the setup documentation refers to running scripts that don't exist, which makes it hard to follow), but it looks like there may be some quirks that are required to get the ros_qml plugins available within QML.
The dependency on Qt 5.4 is also much newer than the default version of QT that is used by most versions of ROS. (Versions before Kinetic used QT 4.x , and Kinetic uses QT 5.3: http://www.ros.org/reps/rep-0003.html ). It's not possible to use multiple versions of QT in the same application, so you'll want to make sure that QML is compatible with the version of QT that's used by rqt before you start experimenting too much.