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Good to see you on here, Mercurius!A bit more on why I think FR is (far) more unlikely than GH, and even maybe that it would be unwise for WotC to publish Greyhawk.
If they go with "Greyhawk classic," they'll make long-time fans happy, and maybe bring on a few new fans, but it is likely too different from contemporary D&D to please the new fan-base. The effect would be somewhat similar to playing an old black-and-white film to a Zennial. Maybe a very small minority would like it, but most would find it too old-fashioned and dislike the lack of color.
If they created some kind of "new Greyhawk" with contemporary sensibilities in mind, they would upset the long-term fan-base, and probably not be offering anything substantially new to the larger base that they couldn't find in the Realms or Exandria.
Of the two, I think the former is the better choice - but probably doesn't make good economic sense, or at least before or instead of the Forgotten Realms.

A while back I pitched an idea for Greyhawk in 5e which would be focused on the thing that grognards & newbies have in common – we all love to world build (pretty sure polls confirm that homebrew worlds leads over FR in popularity).
I don't have my old post handy, but in it I dug up a bunch of quotes that ENWorld compiled from Gary Gygax in which he described his design intent behind Greyhawk being leaving lots of space for the DM's own creations. A "Greyhawk" book might, yes, include Greyhawk the setting as an example, but also really double down on the idea of it being a world builder's supplement. I'm imagining books like Worlds Without Numbers with an OSR influence where random tables, light hints, and bullet-points of possible answers to mysteries are presented as fuel for a DM's own creative spark. So, yeah there's Furyondy and some of the politics around the Shield Lands, but there's even more resources for a DM to "fill in the blanks" themself.
Not sure about the state of legal affairs regarding Greyhawk. I recall Robert Kuntz alluding to some of that on his posts here, so this might all be a pipe dream, but I wonder if this approach might be mutually agreeable to thread some kind of legal needle.