Thanks for sharing these videos! I'll jump in: I recently learned of fretted microtonal guitars - even models made with Legos. Fascinating!
Any (intentionally ?) microtonal accordions out there? Or accordions with unique musical temperaments?
A subject near and dear to my heart too. Being able to play in the temperament of one's choice without re-fretting is one of the advantages of the violin (and of computer-generated sound) that I wish was easier to apply to other instruments.
It seems to me that something like Eivind Groven's microtonal organ should be possible for the accordion. (12 keys per octave, connected to 36 pipes per octave, via a selector that, essentially, asks you what the current tonic is. We have the usual 12 equally tempered tonics to choose from. The tonic, major second, fourth, and fifth are left alone. The major third, sixth, and seventh are flattened 20 cents. The minor third, sixth, and seventh raised by 20 cents. I don't happen to recall what he does with the tritone and minor second - I would guess lowers the former and raises the latter so that D-F# is a purer major third and C-Db is wider than Db-D, when in C.) We already have LMMM accordions - "all" we need to do is add a new kind of register plate, that opens the appropriate combo of M holes.
But I've never seen one. (Nor have people built very many copies of Groven's original organ - all the modern replicas I know of use electronics to automatically apply the pitch bends, not mechanical linkages to sharpened and flattened pipes.)
And, for those of you unfamiliar - Groven is a much underrated 20th century composer. He collected Norwegian folk tunes, sort of the way Bartok did in eastern Europe, as well as writing pleasant tonal music in the standard tuning for full orchestra and brass band.