I think you misunderstand Greyhawk's version of low magic. The PCs can still be magical but the world isn't. The PC cannot pop along to the local wizard school in the village to stock up on potions. Nations have a court wizard or two, and some of the larger nations even have wizards among their armies and navies but the population views them as awe inspiring and unnatural.I gotta say man, I think approximately 0-10 D&D players are interested in a setting like this. Grimdark pre-war? For D&D? Are you even slightly serious?
Grimdark is already like, targeting an old people audience, frankly, grogs and aging edgelords. D&D is absolutely terrible at grimdark. There's no reason to engage with the politics of any of the Greyhawk nations as they're all pretty lame. This is a recipe for selling like hundreds of copies instead of thousands, let alone tens of thousands or millions. It would probably sell worse like this than catering to the ancient fans, even, though I admit not a huge amount worse.
I strongly agree with your general suggestions, but the world you outline doesn't seem one likely to attract players now, in 2021. In 2003 or something? Sure.
In D&D? I don't buy it. I don't buy that that audience really plays TT RPGs, or if they do, wants D&D to be like that. And D&D is extremely bad at that because of the Vancian magic system. The idea that you can have "grounded low-magic" when people are daily summoning magic animals and shooting fireballs and so on at level 5 is pretty silly imho.
But that's not what D&D is about or like, even slightly. D&D is inherently high-magic, and the only way around it would be to literally cut every single full-caster class from a setting, at which point, it's not really D&D.
As for Greyhawk, I think the only way it comes back and actually sells any copies if it's a modernized gonzo dungeon-crawl fantasy setting leading with strong visual design, an appealing suggestion for how campaigns there should basically work, and one that differentiates it from other "generic fantasy" games, and where the strong villains are used to provide adversaries for adventuring, not fodder for politics.
There are many temples but very few truly powerful clerics. Powerful druids form mysterious cabals and become hermits.
Places dominated by magical beings generally suffer as a result. The main villains are magical.
Greyhawk City was always the exception. Full of unusual races, ambitious casters, as well as many martial characters.