C++ can subclass gui::SceneWidget to override mouse and keyboard events; Python needs to have access to this, too. Having mouse and key events would enable things like:

• changing the key navigation if you have an international keyboard (Different Keys in Visualizer to set FoV for qwertz Keyboards #1893)
• custom editing of selected points (Manipulate position coordinate of sphere by key events #1965)
• synchronize cameras with multiple SceneWidgets (Multiple viewports per window #999, see last comments)
• showing the current mouse coordinate (there was an issue for this, but I can't find it)