(I don't suppose I'd getaway with a "will it come in fretless?" twice in one thread...?)
This is interesting. I attended a masterclass on upright bass in classical Arabic music, of course on a fretless neck all the quarter-tones are doable, and it turned out to be very exciting. It takes some getting used to, the modes - maqams - sound very strange at first. Also they are not really "quarter tones", but more like "3/4 tones", in the sense that sometimes you divide a minor 2nd (like A-C) into two halves (instead of three half-steps). I'd give a bass like that a try. But they should have made the extra frets a different color. For guitarists specializing in Arabic music, adding quarter-tone frets is common practice.
