I think Chap has the real point. The EModE gambit is a punt, icing the puck, kicking the ball way down the field. The other team may then get the possession but at least they'll be starting from a lot farther away from the goal, so the defenders get breathing room. The Book of Mormon is just too obviously a crude 19th century knock-off Bible. The EModE gambit tries to rebut that obvious charge decisively by proving that, whatever the Book of Mormon may be, it definitely wasn't a 19th century knock-off of anything.
As far as I can see, though, the belief that these typically early modern syntax patterns are a proof of anything is based entirely on an embarrassingly basic misunderstanding of linguistics.
Grammar is unconscious: native speakers of a language learned in childhood follow the right rules unconsciously, and recognize right and wrong grammar instinctively, without any conscious understanding of what the rules are.
Noam Chomsky wrote:Colorless green ideas sleep furiously.
It's a pure nonsense utterance, and one that nobody had ever heard before Chomsky made it a famous quotation, yet every native speaker of English knows immediately that it is well-formed grammatically. The unconscious nature of native grammar is indeed the foundation of modern linguistics. Lots of quantitative experimental studies show that non-native speakers who learned a language past a certain critical age never attain the speed and accuracy of grammatical judgement that true native speakers all seem to have hard-wired, even if these non-native speakers are so fluent that nobody can tell their normal speech from native speech. Even if the later learners never make errors themselves, they don't recognize subtle errors as quickly and surely as native-speaker children.
In absolutely no way at all, however, does the unconscious nature of native syntax mean that human brains are incapable of generating utterances that do not follow the syntactic rules of their native dialects. All it means is that when somebody does form a non-standard sentence there will be a little Grammar-Nazi piece of their brain commenting, "That isn't right." If the rest of the brain says, "I know, I'm speaking weirdly on purpose" then the Grammar-Nazi piece of brain just says, "Hmmph." People can speak nonsense, they can learn new languages, they can play language games.
And people can imitate other dialects deliberately. Nothing in linguistics says anything whatever against these obvious facts. And nothing about the unconscious nature of native syntax is even relevant to what happens when people are deliberately trying to speak outside their native dialect.
Mentioning the unconscious nature of native syntax in this Book of Mormon-EModE context is nothing but snow. Nobody has ever suggested that Joseph Smith wrote the Book of Mormon in his own native dialect. Instead, as Chap says, everyone's immediate thought is that he was trying to imitate the King James Bible—and doing it badly. So the unconscious nature of native syntax is completely irrelevant to the Book of Mormon. It's not written in the native English dialect of anyone who ever lived.
From following some discussions on Mormon Dialogue & Discussion Board among ostensibly educated people, however, I really think that a lot of the popularity of this Book of Mormon EModE thing is based on letting people think that it is a proven fact of neurolinguistics that Joseph Smith's brain could not have produced Book of Mormon syntax because syntax is unconscious. Making that claim, or even saying things that sound like that claim without immediately clarifying, is either deliberate deception or embarrassingly basic ignorance about the foundations of linguistics.
I'm afraid I lean towards the ignorance as the true explanation, even though some of these people have PhDs in relevant fields. It is possible to get a Ph.D. by mastering technical details while retaining childish misconceptions about one's subject.