Importantly, most of the discourse about ATLA and LOK came out well after the original series ended. As in, YouTube content creators--who are the bread-and-butter of Gen Z and Gen Alpha--talk about it constantly. In essence, we have a very unusual situation where the media of the generation that preceded the current one(s) has been preserved, in a way that normally doesn't happen, because the relatively new medium of video essays, LPs, reaction videos, etc.
It also matters, I think quite a bit, that Millennials were kinda spoiled for great TV adaptations of existing works (e.g. the DCAU, ATLA, Samurai Jack, Animaniacs, Gargoyles, Courage the Cowardly Dog, etc., etc.), widely-beloved educational media (Bill Nye, Carmen Sandiego, Arthur, etc., and arguably films/miniseries like The Civil War and Apollo 13), and a spectrum of other things.
Steven Universe, She-Ra, MLP, Infinity Train, Voltron, and The Owl House are major ones I know of that are varying degrees of "more recent," and I'd expect all of them to have a meaningful impact on the kinds of things Gen Z and Gen Alpha are looking for. Maybe Legend of Korra as well, though even for younger generations, I don't think it has landed quite as well as the original did.
Notably, these shows often feature predominantly female casting (SU, She-Ra, MLP), numerous female main protagonists (She-Ra, MLP, some seasons of IT, TOH), implicitly or explicitly LGBTQ/nonbinary/asexual characters (sometimes including main protagonists), explicitly non-white central characters if the characters are humans (Korra, TOH), more direct and empathetic representation of neurodivergence (e.g. characters who are explicitly or implicitly on the autism spectrum or AD[H]D), and a penchant for forgiveness (albeit not necessarily redemption) of characters who have been more self-sabotaging than cackling-madfolk evil rather than passing final judgment even if the things they've done have been pretty screwed up (SU, She-Ra, Korra, to a certain extent MLP).
I would expect all of these to factor in to their preferences. Literary stuff seems to be moving in similar directions as well, e.g. what I've heard about the Percy Jackson books, the Hunger Games books, the Locked Tomb series, and more.
This is...potentially going to have to cross swords with some of the assumptions baked into the Greyhawk concept, like innate humanocentrism/humanosupremacy, which won't appeal to folks who enjoyed most of the TV shows I mentioned above (I'm pretty sure Korra is the only one that has exclusively human protagonists? The spirits are allies, bystanders, or enemies, never central characters.) Anthropomorphic animals, humanoids with clearly nonhuman characteristics (e.g. Scorpia), devils/demons as deuteragonists, literally talking ponies...Gen Z media embraces a very wide range of nonhuman entities as equal or even superior to humans.
We can also look at negative influences. Game of Thrones was a big deal...but it crashed and burned, HARD, which may sour a lot of people on the constantly grim-and-gritty realpolitik angle that some of Greyhawk leans into. Superhero media has taken a pretty steadily "grime it up" approach since at least The Dark Knight and possibly earlier, and multiple generations are kinda sick of having "heroes" in name only and "villains" who are often significantly more sympathetic (or, worse, a black-on-black morality where your choices are "serial sex offender and murderer" vs "heartless 'I did what I had to' underground rebel" and anyone who shows a lick of human decency rarely lives to regret that choice, e.g. The Boys.) Nuance is good--and we see that in things like Invincible--but so much of "nuance" has been either ham-fisted or bad-faith over the past two decades.
So...I think I have to echo the overall sentiment: What, exactly, in Greyhawk is particularly appealing? Because I think there's major potential for this to blow up in WotC's face if they handle it wrong. If the old fans feel 5e Greyhawk is a sanitized, kid-gloves "no judgment allowed" zone, they'll turn on it faster than you can say Gary Gygax. But even that much change might be a major turn-off to current teens and early twentysomethings who are likely to desire cultural inclusivity and physiological/behavioral diversity.
I've been wrong about plenty of things in my life, so I wouldn't be surprised if I'm wrong here, too. But I can't shake the feeling that WotC is banking on "it's Greyhawk, the old hands love Greyhawk, they're guaranteed buy-in, so we can focus on courting the new fans," and...well. As said, I foresee that blowing up in their faces.
