We don't need a metaphor. We simply need a "menu" that shows up when you're holding Ctrl that lists the possible continuations of the shortcut along with brief

We don't need a metaphor. We simply need a "menu" that shows up when you're holding Ctrl that lists the possible continuations of the shortcut along with brief descriptions. I think being "intuitive" and being easily discoverable are not the same thing for UI, and designers pay too much attention to the former while ignoring the latter. For example, command line options for Unix programs are not intuitive at all, but they are very easy to discover via a standard mechanism that most system users are familiar with (man). Good interfaces communicate thing to the user. "Natural" interfaces only use things that have already been communicated or otherwise learned, which makes them much less flexible.