Nagarjuna's reasoning is correct, based on his presumptions.
...if “we strip away the non-essential” fully, we are left with nothing.
Or, more precisely, we are left with "no thing," which would not be the same... thing... as absolute nullity.
You could take the position - and on reflection it would be a quite arguable position, if not necessarily a practical assumption to guide research - that the essence of thinking, what we ought to think of as thinking truly, must always finally evade detection, or must be that which detecting cannot detect, because it is already the detecting. So the business of cognitive science will be to strip away what is non-essential to thinking and confine it to the realm of mere things. The science as opposed to the philosophy of thinking would be a continually pushing away of its object by closing in on it - or an endless series of potentially interesting failures. So, like every other science, only especially so. Or: Since "science" could stand for "thought," any science of science would be infinitely regressive meta-science, science of science of science of science ad infinitum. For the long version I'm afraid it would be back to Hegel or maybe to some of your Buddhist buddies.
I guess the implication is that them brains is turning out differently than they might have been expected to turn out otherwise - the main takeaway being that the condition of blindness correlates with objectively measurable or detectable organic differences in brain structure, whatever terms you apply to them.
I was interested by the article in part because I have frequently seen people asserting that the traditional claim regarding enhancement or alteration of other senses was a myth. Also interesting that changes in memory and language processing are also detected.
Would of course also be interesting if other "re-wirings" were detected. When I was reading up on cognitive science or neuroscience years ago, it was my understanding that one of the premises undergirding them/it was that every change in mental or subjective state must correlate with an in theory detectable alteration in physical state - that every thought is also a thing or is thingy.