Paul, that's really cool.
When I tried to build it I found that the actual enclosure is a big part of the ebow's design, I think that now that you've found out about those 'positioning magnets' most of the details are revealed. I don't see why it couldn't be done with all sorts of variations and mods. I potted the coils with super glue, that helped a lot in making it stable, and I used thicker wire for the output coil to be able to get a lot of turns with little dcr. as for the shape of the whole thing, that was the tough part, I did mine using black bondo paste. If I were to make another one I'd probably use a single AlNiCo pickup pole piece cut in half for the coil cores and magnetize it after assembly to try a few polarity combinations, it is critical that you get the winding and magnet polarity correctly for it to operate.
Once you know the dimensions it's a pretty quick layout, there aren't that many parts or choices as to where to put them.
The switch does intrigue me with the harmonic and regular modes.
IMO the ebow is as elegant as it can be, and I'm sure I'll buy one as soon as I'm able.