An organ pedalboard MIDI controller would be an off-the-shelf solution albeit expensive. You could hook it up to a drum rack in a DAW in order to remap the pedals to a useful layout.
With a foot activated MIDI controller the number of keys will always be rather limited. Therefore, I think that the virtual layout should be customized to the music you play or even for each song. E.g. you could only map notes of a certain scale and range in order to save space.
If you consider building something custom; I have found that outputting to hardware MIDI from an Arduino is delightfully simple. (The hard part on my own project is finding motivation for figuring out how to read velocity from piezos and isolating vibrations.)
Organ pedalboards require sitting down and so are not really what I want.
The number of keys is the real problem - I don't want to be playing a single note in one octave, I want to play my chord progression and that means I need separate buttons for the major, minor, 7th (which 7th...) for the chords that go with the song.
A medium number of keys could work out by using a custom layout for each song as many songs don't use too many chords. Similar to tuning timpani for each song.
With a foot activated MIDI controller the number of keys will always be rather limited. Therefore, I think that the virtual layout should be customized to the music you play or even for each song. E.g. you could only map notes of a certain scale and range in order to save space.
If you consider building something custom; I have found that outputting to hardware MIDI from an Arduino is delightfully simple. (The hard part on my own project is finding motivation for figuring out how to read velocity from piezos and isolating vibrations.)