I have to say something very controversial, but I do say it as an old-timer with much love for both Faerun and Oerth:
Greyhawk really isn't that different from FR.
Difference in level of detail? That's really not a big difference. Liches with armies? Both have 'em. Mad reclusive wizards? Check. Secret racial supremacist organizations? Check. Big waterfront town that dominates the setting and the region's trade? Check.
Much as I love Oerth's history, and its Leiber- and Howard-esque origins, I don't think you could draw a hard line between the two and show a huge self-evident difference.
Dragonlance would be in a different boat, though a slightly similar boat. At least we had the Cataclysm and the divine isolation, and the magic moons, and the LotR-esque elements, but still somewhat classic fantasy.
Dark Sun is an example of self-evidently different. The minute you're fighting with a bone sword back-to-back with your six-armed insect-man ally, against a tribe of cannibal halflings, while your party wizard is sucking the life out of the ground and giving you body aches in the process just to cast magic missile, you KNOW you ain't in Faerun anymore.
Eberron is another - golem-men detectives interacting on lightning trains with good-aligned blood-priests while solving a whodunnit before going home to his two-mile-tall Mega-City while his friend with the inherited magic tattoo cuts a trade deal with a medusa diplomat from the next-door monster nation, that also screams a different brand of fantasy.
Much as I'd like to see Greyhawk goodness, and find out if Iuz still has his nation, or see a mega-adventure dealing with the mystery of the Invoked Devastation and Rain of Colorless Fire, it doesn't scream "drastically different fantasy" from Forgotten Realms to me.
From the podcast it sounds like Mike Mearls is wrestling with: "Greyhawk as originally conceived wasn't drastically different from FR, but how might we focus on unique aspects of the setting (while still staying true to its old school roots) to make it shine as something distinct?"
I'd say there are 5 things that could take center stage in a Greyhawk adventure-setting.
1. Greyhawk was a setting discovered through modules. It was about Playing the Game more than having a setting bible, and embracing the way each group's players created alliances with orcs or established strongholds outside Hommlet. And it had a big Living Greyhawk convention presence IIRC. Keeping that approach seems to fit WOTC's current model of adventure-based releases...and could be blended with some kind of organized play initiative.
2. Greyhawk has lots of sci-fi elements; there are crashed spaceships, spacefaring races like the Neogi, and people like Murlynd walking around with non-steampunk guns. Also, the Far Realm serves in a more classical Lovecraftian sci-fi vein, rather than the more supernatural bio-tech take that Eberron has. There was a gonzo quality to Greyhawk that, if approached fresh, could actually be portrayed as some kind of sinister outsider presence.
3. Greyhawk always felt more "middle fantasy" to me than other D&D settings – politics, intrigue, & human/humanoid relations took center stage, and when monsters/magic appeared they were truly monstrous/magical to the NPCs. There was a distinctly feudal pseudo-European feel to the setting, and at times there were glimpses of a dark Arthurian fantasy. If any D&D setting could be described as Game of Thrones-ian, I would say it's Greyhawk.
4. Greyhawk seemed to bleed into war stories at several points. I was never deeply into the From the Ashes story, but I wonder if there might be something in there that could make Greyhawk a war story distinct from Dragonlance's War of the Lance. Somehow, I associate books like The Black Company with feeling at home in Greyhawk.
5. Greyhawk has lots of sword-and-sorcery elements thanks to Gary's love of Leiber and Howard. I wonder if there might be a way to play that up while keeping it distinct from the grim sword-and-sorcery of Dark Sun.