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I think the whole point is that as long as the nut and bridge are rigidly separated then what is separating them isn't that important in terms of tone (certainly compared to pickup position) the strings have a node at each end and the movement of the string relative to the pickup creates the signal. For hollow-bodies it may be more complex inasmuch as the brigde may not be purely a node and energy that the string puts into the body as a result may be returned to the string later.
Also worth noting that the video infers that literally no body, sounds just as good as ash or whatever, but although there in only air in the middle of that experiment, each end of the strings are anchored via the bridge and nut and tuners to massive heavy wooden workbenches weighed down with motorbike engines. Anyone who’s ever leant the headstock of an unplugged electric or bass up against a wardrobe, table or stud wall will tell you that resonance doesn’t have to come from the mass between the neck and bridge.