It seems to be quite doable. in spite of handlers having been designed for 2D. We can add 3D coordinates to QQuickHandlerPoint, and have them populated only when relevant: that's a way to expose 3D QEventPoint positions to QML.

QQuickPointerHandler's target and parent properties are both QQuickItem* though. Code that assumes it will be of that type and not null needs work.

A harder problem is getting handlers' built-in behavior working: e.g. DragHandler only knows how to drag an Item. Dragging other kinds of objects can be done via bindings.