I just found some Turkish classical music using nylon string guitars with microtonal frets inserted into the board or an adjustable fretboard. Wow, I have never seen this before, movable or insertable frets on traditional instruments, but two/three string mini-frets to properly play music derived from Turkish music theory or totally movable frets applied to shim the different tunings from different classical periods to play Bach? Nuh-unh, that's a new one, and it is pretty amazing.
Turkish classical music suite-
Bach's Goldberg Variations on a classical guitar with adjustable frets and assorted tunings-