It is a matter of speed. The MPlane command is pretty good, but it takes too much time to hunt for the little widgets which represent different MPlanes and to click the widgets. We need something that is almost as fast as the OneView command. I believe that the best way to speed up the custom-made CPlanes and MPlanes is to temporarily display them on the screen as fairly large icons similar to the world axes icon.
If you improve the user interface, you may as well improve the world axis icon: Flaws in world axis icon