A lot of it isn't new, but this quote did jump out at me. "Other factors we consider are things like ‘Do we have an idea to sufficiently differentiate this experience from the other worlds?’"
See that? That's why every setting book they put out has a hook or gimmick to make it unique, and that's why there's no Greyhawk book on the release list.
To address this, let's look at the 5E settings so far, and what--in a word or two--differentiates them from other worlds:
Forgotten Realms: kitchen sink galore
Ravenloft: gothic horror
Eberron: magitech/steampunk
Ravnica: mega-city
Theros: ancient Greek themes
Wildemount: Critical Role/contemporary themes
Strixhaven: magic school
Spelljammer: space fantasy
Dragonlance: meta-story focus
Now let's look at some past settings that haven't received 5E treatment:
Dark Sun: post-apocalyptic/sword & sorcery/desert-focused
Planescape: planes
Birthright: kingdom building
Council of Wyrms: dragon-focused
Mystara: bearded elves
Nentir Vale: points of light
Comparing the two lists, one can see how any of the first three options would offer something significantly "new" to 5E, though Birthright is obviously far less likely than the others.
So what would set Greyhawk apart from, say, the Forgotten Realms? Well, we can start by saying what
wouldn't: doubling down on yet another kitchen sink setting, including both "every real world pre-modern culture has an analogue," but also "every aspect of D&D lore finds its way here, as written in the PHB and splats."
Greyhawk could differentiate itself by emphasizing its old school qualities, being more sword & sorcery than epic/high fantasy, and being a "twist" on kitchen sink, aka "themed kitchen sink." Meaning, it could take an approach similar to Eberron rather than the Realms: quasi-kitchen sink and strongly thematic.
So while I agree that GH doesn't have a clear and obvious hook or gimmick that sets it apart, D&D settings aren't only about gimmickry, but creating a themed context for adventuring and/or reading. So if anything, that quote implies that if they were to publish GH, they'd emphasize its "Greyhawkian" (and thus, Gygaxian) elements.
That said, we can only speculate so far on whether or not WotC will publish Greyhawk--not to mention Dark Sun or other classic settings--until we know more about the "new settings." I mean, if one of those settings has strong sword & sorcery and pulp elements, then Dark Sun, Nentir Vale, and Greyhawk might be seen as superfluous. Or if they take a completely different approach to the planes, then Planescape would be off the books. It may even be that one or both of the settings takes elements from certain classics and remixes it in a modern idiom. For instance: A post-apocalyptic, points of light setting involving pushing back monsters and building micro-kingdoms, set in a setting modeled after Persian and Indian myths. Meaning, touches of Dark Sun, Nentir Vale, and Birthright, yet in a non-Western context.
