Guitar made from concrete.

[Sonic Mountain]

I’m on holidays and not going to try and dig up articles on my phone, however the principles of electromagnetic induction are pretty simple. The vibrating steel strings in the magnetic field of the pickups induce a current in the windings. This is the signal that is sent to the amp and boosted. The same principle then takes place in the speaker where the signal is converted back into vibrations, which push the cone creating sound. The wood simply has no effect in this process. The string vibrates between the points it contacts on the bridge and nut. Those materials may affect the vibration and sustain of said vibrations. The wood these things are mounted on does not, even if the body does vibrate, these vibrations cannot the be picked up electromagnetic induction process. Any vibration of the body feeding into the string vibration would be so tiny as to be imperceptible in a solid body electric. A hollow body or electric acoustic may develop some microphonics, due to the large internal cavity, however such additional signals are generally considered undesirable and do not make for nice ‘tone’ rather hum and feedback. That’s my take on it anyway.

[JimC]

principles of electromagnetic induction are pretty simple. The vibrating steel strings in the magnetic field of the pickups induce a current in the windings..

Of course none of that is wrong... When I learned, however, from amplifier designers that the design of the speaker cabinet has an effect on the behaviour of the output stage of the amplifier I started to realise that music amplification was an awful lot more complicated than I thought. The question boils down to whether the vibration patterns of the body have an audible effect on the vibrations of the strings, and how great that is.
The apparent existence of the phenomenon of bass guitar neck dead spots, for example, suggests there is some audible effect in some circumstances, but I haven't come across anything to actually put numbers on.
Maybe I should make an instrument with interchangeable bodies and try doing some tests.