with the straight tool, you press and hold 'shift' for staright lines. that method could be used for squares, ellipses and other shapes. hold say 's' for squares/rectangles, 'c' for circles etc
but what would then be good after those are implemented would be a 'edit keystrokes' menu. should you could then choose which keys would be suited for which ever shortcut.
namely because not everyone uses QWERTY, so the option of making your own keystrokes shortcuts would be very powerful productively.