Well, actually I'm coding a debugging overlay to show entity labels. As a debugging tool, this node doesn't know when a camera change may take place or when the debugging node should abandon the current camera (maybe because it has been queuefreed. My goal is to make the debugging tool as reliable and efficient as possible.
The camera_entered signal is triggered even if the new camera is not the active one, so I can't use this approach to detect active camera change.