And I think it's a reasonable idea, especially for studying, practicing, or sight reading. I'm current struggling to map staff notation onto the guitar fretboard (I can play piano from staff notation, and play the guitar "by ear," so I'm trying to synthesize the two abilities), and I think this might make it slightly easier. For a lot of classical guitar transcriptions, or any guitar transcriptions that refuse to transpose (an octave), there is a lot of extreme ledger lines, and the shapes would help immensely.
If you're choosing between "rewrite this guitar music to transpose so there aren't crazy ledger lines" vs. "rewrite this guitar music into a radical new notation system", I think I'd go with the first choice.
Standard notation for guitar music also suffers from the "where on the fretboard do I play this" problem -- sometimes there are hints (like finger numbers), but often you just have to try a few options and see what's best... which is rough going if you're trying to sightread a piece you don't know yet.
TAB notation, of course, fills in the missing info on suggested finger placement, but omits other essential info (rhythm!), so by itself that's also broken....
