Being a devil's advocate is by definition being at cross purposes.
I don't know about continuing further. The ideas are developed already, and useful in reading, but I haven't gotten enough control of them to use them in composition.
So far as I understand it, this thread was at your request and for the specific purpose of explaining the background of my thinking that lead to the assertion that ἐστίν had moved for a specific purpose. Perhaps enough has been said already, to show that I am of the opinion that there are two speech styles present in Koine Greek, and that far from becoming a debased form of the language lacking the range of styles that Classical Greek had, there is a structured and alternating set of two speech styles, and that the abstract element comes first, and the concrete one second. So far as I can determine, γεννᾶν belongs to the abstract / general group, which puts it in the first half of the thought (thought being that verse in this case).
If it is gammatically part of the second part of the phrase, but in terms of belonging to either one of the moieties, it is a word that is known and used (exclusively collocated) with the abstract / general moiety, then it seems that in this case, the word's attraction to the first (abstract / conceptual) part of the phrase has pulled the ἐκ πνεύματος into the first position of the second (specific / concrete) part of the phrase, where an adjective should be. (In answer to the question that I assume you are asking, yes, πνεῦμα seems to belong to the second (concrete) moiety). Rather than the ἐστίν following the adjective and preceding the prepositional phrase, the attraction (based on membership of the moiety) of the adjectival preposition to the left pulls the next element into the first position of the second half of the phrase - the predicate.
I wonder if enough has been said already, that at least it can be recognised that there was a basis of reasoning for my explanation to Alan? And that basis of reasoning was based on a two-fold classification of the vocabulary of Koine (I can find the older pattern which is preserved in Koine Greek in relative phrases and after some discourse markers in Classical Greek, but not the structured alternating moieties that are so clearly in our period of the language)?
If enough has been said then this thread has served its purpose, and I can go back to thinking about the syntactic vs the lexical function of prefixed prepositions. The moieties stuff is last year's thinking and boring already.
Jonathan, have we said enough that with or without evidence or proof being presented in full or partially, and with others either understanding, partially understanding, or not understanding what I am talking about, I at least for my part can see (have found) an overal pattern in the vocabulary, or at least I make the claim that I can see (find) an overal pattern in the Koine Greek language, associating certain vocabulary elements with either of two speech styles, and that I can identify, or at least that I claim that I can identify words as belonging to one group or the other? If that at least is clear, then I think enough has been said.