This might be very cool on a Chapman Stick.
One guy is using nylon strings on a Strat.
Check out the videos.
https://www.youtube.com/@Light4Sound/videos

I wonder if this design can be modified
to trigger equipment such as the GR-55?

I wrote to them a few months ago. Very responsive, but spacing is probably going to be an issue currently.
I didn't get far enough to ask abt depth b/c the spacing issue sort of killed it

I didn't get around to hex either. being optical I SUSPECT crosstalk would be negligible if it exists at all which could make synth triggering further toward the neck practical (larger string excursion allowable)
but the possibility of low cross talk might be nice for general use too

but, like so much. I don't know if stickists are a large enough market to warrant modification..this is, again, a suspicion , but I'd expect the spacing to be pretty much in granite on a PCB

there are a few other optical systems(lightwave has been around for years) but ther hasnt really been the adoption...then again we play Chapman stick so that's not exactly alien to us!!