If the purpose of abstraction is to get as far away from representative forms as possible, then the ultimate abstraction is something that's totally unrecognizable as anything. In the 1950s, Abstract Impressionists went to such lengths to avoid even suggesting the use of paint that judgment of their work was based on how many millimeters the dried pigment rose above the canvas.
Such a radical interpretation implies the existence of a "norm," which, in the case of music, takes in everything from scales to instruments themselves. If so-called electronica has done anything other than allow dance music artists to tour out of their Powerbooks, it is that it has pushed abstraction to its limits.
Beyond a certain point, however, can you still call it music? Some schools of digital thought in Europe -- the Sonig crew in Germany and a few artists signed to England's Warp label -- seem to exist for the purpose of challenging people's ideas of where music ends and noise begins. Skist sort of subscribes to the same idea, but with one difference: vocals. Even when it avoids conventional melodies, the human voice is itself recognized, at least subliminally, as the source of all music.