But if we anticipate that more states might be added in the future—or if the backend might be swapped out for one that has more states or an unbounded number of states
It is quite possible. But:
- The current OSD design can't handle an unbounded (or large) number of states, anyway.
- If you are going to use the mouse (because there are more states than can be comfortably cycled through by keyboard), why not just click the tray icon, which doesn't require a hotkey upfront?
- So I think the OSD should differentiate from the applet, not duplicating it. If there are going to be 10 states, probably the OSD should only show (and cycle through) 3 of them, which conceptually resembles the current 3.
If you look at the volume OSD / applet / KCM, they form a ladder of simple to complex, not duplicating each other. I think that's a good example how an OSD should work.