Most impressive 
Really creative UI design - I really like it.
My first thought was to swap the UI around a little bit and place the main playable controls on either side of the Grid so you could pick it up and play it, perhaps a little like an accordion; but having tried it itās really not that comfortable to hold and play at all like that (at least not the walnut version in my hands). The second row in is most comfortable to reach but only for a few buttons. Having said that, perhaps it may be an idea worth exploring a little?
Second thought was to put the tunings on a second page, not sure if that is possible with GridOps?
Finally, how about treating the columns as frets, so the lit buttons are actual guitar chord shapes? Would you need to hold the chord down? Perhaps a separate hold button so you can hold the chord shape after you have removed your fingers. On release, dampen the sound with a LPF / VCA and pitch shift down to default string tuning - kind of like what would happen if you released a chord on a guitar.
Apologies if any of this is totally impossible with whatever you have done so far, I can see how some of it might be tricky to implement, itās just some random ideas.
Once again, I really think this is great - good work - Iām looking forward to trying it out and reading your scripts 