Evenif we're talking about the niche-st of the niche-st things here, I'm still kinda surprised nobody has ever tried this more seriously after the Synthaxe. Maybe they were afraid to fail as miserably or so. But I could pretty much imagine this to work on existing guitars as well (replacement neck, frets or some clever sort of inlay/overlay), so the risk of completely burning a lot of your money would be considerably lower.
I only played a Synthaxe once, tons of moons ago, but I still remember how remarkably killing the tracking was, compared to my GK3/GI-10 combination. Apart from some things that just don't translate well in guitar-to-MIDI land (such as scratches, slides, rakes, some bends, etc.), you could almost play normally and didn't have to go for a super clean technique. Guess I'd buy a replacement neck with pre-cabled electronics more or less in a heartbeat.