Since I know you dislike point-by-point responses,
@Snarf Zagyg, here's my best effort at one that responds to the whole while still (more or less) responding in sequence. Hopefully you do not feel I have misquoted you, in places where I reference or paraphrase your post.
As sort of a foregoing thing...you never actually explained why it is
imperative for D&D to get a new publication of GH. You explained why it's relevant as a historical artefact, and gave explanations of how it differs from (some) other settings both recent and long-standing. But I don't really see an explanation for how
imperative it is to do this. You've done quite a bit to say what form the GH setting should take in 5(.5)e, and why it should take that form and not some other form, but not really explained why it's
imperative.
Moving on: I have little to say about the history because much of this is either outside my experience, or something I have already heard elsewhere, so I leave most of that aside. (And, to be clear, I did see your facetious note about Dragonlance, so yes, I did actually read the whole thing!)
I would, however, like to make an important note: I find it unusual that you are so dead-set on the
need for an ignorance of what lies beyond the horizon, whether that be a physical horizon ("no one can be sure what else is even on the world beyond the eastern part of one continent") or a temporal horizon ("What is the real story behind the Rain of Colorless Fire and the Invoked Devastation?") I find this unusual because, in many of our prior interactions, you have heavily prioritized the DM
having firm, binding answers to these sorts of questions, to the point that it becomes difficult or even
destructive to have anything be introduced that does not fit in with those answers. This is, perhaps, a question better answered in another thread. But I find it curious that you think it unacceptable to nail down more than a small part of a large world in one sense, and absolutely essential to nail down essentially every part of a world in the other.
At one point, you said, "You can't cater to angry people." I find this a curious notion, particularly given that 5e itself was very intentionally catering to angry people. Would you be willing to unpack this further?
For your overall point 3, my only responses are, firstly, that I'm glad you included 3A ("not simply faithful to the original") because that is absolutely a serious trap any highly traditional effort can fall into. Being forward-looking (e.g. focused on fostering new fans) can be a difficult thing to do when focused on revitalizing an old and storied thing. Secondly, I certainly hope that they choose either the first or fourth option on your list. For my part, the second and third are effectively the same thing, just whether "the evil" has
already won or is merely
beginning to win. Neither of those is, IMNSHO, likely to bring in lots of new fans. If the world sucks and is miserable, people are liable to tune out; this was part of (though far from the only part of) why the GoT TV show's final season did not go over well with fans. It would also be a big question as to why one would get in on this "New Greyhawk," since both of those positions are quite well-served by an already existing setting, namely Dark Sun.
By comparison, the only other setting which hits either the first or fourth points to any serious degree was 4e's implied setting, the Points of Light/World of Nentir Vale/"PoLand"/etc. Humorously, because of your interest in keeping the boundaries of the world unknown and mysterious, this actually means you could cannibalize parts of Nentir Vale into Greyhawk, giving "modern" D&D fans something of a foothold. Nentir Vale shares both the "the great kingdoms are fallen and only a few city-states remain free and civilized...for now" style, and while the world itself is not particularly gonzo, much of its mythic backdrop (the Dawn War, the War of Winter, the mutually-assured destruction of Arkhosia and Bael Turath) paints some pretty big
potential for gonzo stuff.
I think you could get a lot of mileage out of that. The groundedness and tradition of Greyhawk and the modern components and implied scope of Nentir Vale could be a really winning combination.