I know this isn't a keyboard shortcut, but you could just double-click the shape layer tool in the tools panel. As long as no other layer is selected (you can press F2 to deselect everything), it'll make a new shape layer with a rectangle (or whichever shape the tool is set to make) already in it.
Every time you have no layer selected and you click with any of the shape tools you create a new shape layer. I have never had a need to create an empty shape layer but if you do use the menu once and then select the layer and press control/command + d as many times as you need to duplicate the layers.
It is possible to edit keyboard shortcuts but not to create a new keyboard shortcut that does not exist.
You can press the "Q" key to create a new shape layer but only if you have no layer selected in the timeline.