I would be among the first to say that a MIDI guitar is somehow no longer a guitar, but it is a good proof that a piano keyboard is not the center of the musical universe. It is an interesting way to run a synthesizer.
A modeling guitar would be something quite different from a MIDI pickup. Processing each string through a DSP to allow the a guitar to sound like a Gibson Humingbird for one song, then like a 1960's Telecaster for the next would seem to be quite an advantage to me. I wouldn't care much if the body were made out of concrete or polished buffalo crap (so long as it weighed less than my SG). To me, it is more about what it sounds like when I play it. The dimensional stability of concrete or graphite fibers or other potential materials would be a godsend with the room temperature swings that I generally experience.
The depth of our becoming stodgie old fogies is proved out in little things like mshilarious not being able to even get people to listen to how to properly wire an electric guitar. Magnetic coil pickups are not a good way to reproduce sound. We should be looking for something more accurate and flexible.