So it would work on an oud, sitar, and other such eastern and middle eastern instruments. I heard something about microtonal guitars being made, but it must be quite hard to use.
Actually if you read he said he had a special 16 fret guitar made, but not using a 16 note scale. Indian music uses 22 notes to the octave, and usually no more than like 9 notes for a raga, so it is not really the same thing. You need an instrument w/ 16 divisions to the octave to truly play the correct intervals of his "Xavian". That is why he says it is his "own" mode. If you could play it on a sitar or middle eastern instrument, you could probably find the same mode in that music somewhere. I read that Chinese music divides the octave into 60 notes, but they only use perfectly tuned "pentatonic" scales from those for a particular "mode". I wonder if Steve has developed any other new "modes" on his 16 fret guitar.
It all sounds out of tune to my "well tempered" ears. LOL.
On a similar note it is interesting to watch someone play a sitar or Persian setar, they have movable frets to accommodate the mode they are improvising in. That reminds me of the keyboards of the Classical era where the piano was tuned in a temperament for a certain key, and would need to be retuned for another key.
In essence you can say that our Equal Tempered 12 tone scale is 'equally' out of tune with itself!