QML visualization through VTK was abandoned on 8/10/2018.
Due to threading issues between QML and VTK, prop picking in VTK had inconsistent functionality.  Requesting and interacting with prop picking outside of standard VTK calls (i.e. left/right-clicking on filters) was offloaded into a command queue for when it was safe to make prop picking calls.  However, interacting with existing representations and VTK widgets (i.e. vtkScalarBarWidget, vtkImplicitPlaneWidget2, vtkBoxWidget2) could not be offloaded in the same way.  Due to this, mouse interaction with these widgets would sometimes fail to start or stop, and OpenGL errors would be thrown.