This reminds me of something I read ages ago in a guitar magazine. Like any young geek, I would do semi-obsessive research about newly-discovered cool things. One of those interests was heavy metal guitarist Yngwie Malmsteen — introduced to me through a fantasy book, of all the unlikely sources.
This interview contains very similar information to that late–80s or early–90s magazine article:
Hugh: You got the idea for a scalloped fretboard from a 17th century lute, is that correct?
Yngwie Malmsteen: Yes, I was taking an apprentice gig because I wasn’t very big on going to school you know. I tried to get a gig as a luthier. I’m working on guitars for free, because I love working on guitars anyway. Though I did think he’d give me some money but, anyway, this cat came in with a 16th or 17th century lute that was either so worn out or made like that. I don’t know. I’d never seen one. There were no frets, just tapered wood for frets.
Malmsteen goes on to talk a bit more about some of the other experimental designs he worked on. Fender actually makes a commercial model of Stratocaster that has a scalloped keyboard — presumably based on one of those experimental guitars — which Malmsteen mentions in the interview.
Jimi Hendrix also modified many of his guitars to get the sounds he wanted. It seems that high-level performers of any stripe like to exhibit more control over what they produce by creating or modifying their tools, and guitarists are obviously no exception.