That's nice!

That may not seem like an obvious use-case when only thinking about a piano, but since it's mapping MIDI keys to commands, I guess it should be able — or at least no very far from being able — to map ergonomic MIDI controllers to actions that are not as ergonomic with the usual keyboard / mouse / trackball / touchpad most people use.

I wrote what I believe is a similar tool but with completely different goals initially: https://github.com/Arkanosis/smhkd ; I use it with a cheap MIDI controller (namely the KORG nanoKONTROL2) and was considering using another one with motorized faders (namely the Icon Platform M).

MIDI controllers are great for all kinds of non-musical things like: - setting the volume / balance / solo / mute for speakers / multiple headsets and mixing multiple applications (eg. using pactl); - setting the zoom level / brightness for camera / webcam (eg. using v4l2-ctl) ; - setting the source / brightness for monitors (eg. using ddcutil)…

Same. In the past I've mapped cheap midi controllers with endless encoders over to act as a "scrubbers" when doing video editing.

I see I'm not the first to have this idea haha. I suppose you could use additional midi controllers as extra "function" keys, for things like volume control, brightness, etc.. Could be useful especially if using smaller keyboards without a numpad or a function row.