It is currently not possible to register a callback on any class in the rendering-pipeline to get informed when the rendered scene has been modified by zoom or panning.
This used to be possible registering a callback to the itk::MidifiedEvent on the mitk::DisplayGeometry. Since this class has been removed, there is no way to achieve the same effect.
As this is crucial for me, I would like to either mark the CameraController as Modified or emit another itk based event in the method mitk::CameraController::AdjustCameraToPlane(). According to Christoph Kolb, this would be the correct position to add this event.