I read the point as saying that language is capable of greater depth than humans. Das nicht nichtet is a coherent statement despite the objection of the logical positivists, but it is really deep.
As an aside, I'm not persuaded that metaphysicians are saying anything useful. But the objection that their statements were incoherent is a stronger objection.
The interpretation of some of Heidegger's statements as incoherent isn't just something his enemies came up with; it is supported by other statements of Heidegger's (as Carnap notes in his criticism of Heidegger). I really am curious as to what coherent statement you think you can find in "the nothing itself nots."
[I'd put this in an open thread, but those don’t seem to happen these days, and while this is a quote it isn't a Rationality Quote.]
— Geoffrey K. Pullum, Language Log, “Never fails: semantic over-achievers”, December 1, 2011
This seems like it might lead to something interesting to say about the design of minds and the usefulness of generalization/abstraction, or perhaps just a good sound bite.