If I was in charge of Greyhawk right now, with 5th Edition coming out this summer, and the setting itself having officially lain fallow, for all intents and purposes, for nearly fifteen years, this is what I would do with it.
I'd have a three-pronged approach.
The first prong would be traditional RPG supplements; more specifics on those in a minute. The second prong would be board and card games that were set in Greyhawk and which played on what I think are its unique strengths. The third would be a series of miniatures and scenarios specifically designed to play into the upcoming Battlesystem rules that were announced yesterday.
I happened to catch some of the Q&A from last Friday's video broadcast, and was (pleasantly) astonished to see the Wizards of the Coast guys talking about treating settings in exactly the same way I've been talking about for quite some time now. Choose a (relatively early) point in the timeline and make that the "default" starting point in the setting. Then have a tableau of events happening in the background. Any given DM could use or not use those events as he sees fit. Perhaps his players will alter the course of those events.
But doing so means you can't extend the timeline too far. The Forgotten Realms chronology spans more than a hundred years (the Grey Box being set in 1357 DR and the Campaign Guide being set in 1479 DR). It would be nigh unto impossible to provide viable alternatives for all of the major events that the PCs could influence, especially when they interact with one another.
But Greyhawk, right now, only spans fifteen years (the Folio and Gold Box being set in CY 576, and the Living Greyhawk Gazetteer being set in CY 591). There's a lot of history packed into that decade and a half, but it's still manageable. Certainly enough for a paragraph here and there to describe "alternate timelines" that a home campaign could follow. Fifteen years of in-game time seems like plenty to me, but I might take it out another ten years just to make it an even quarter-century. After that, leave everything to the DM to work out (and stick to that promise!).
So the first "prong" of my approach would have a major setting product, based in CY 576. A boxed set with gorgeous maps would be ideal, but a suitably detailed book would do. Then have another product, which I have previously called the Great Greyhawk Campaign (in homage to the Great Pendragon Campaign product), which details not only the historical changes to the setting over the course of the next 25 years, but gives the DM specific tools that he can use to make the setting come alive through those events. Finally, another end-cap setting product, detailing the world as of CY 601, giving DMs who want to start their own campaigns without the detailed events happening in the background.
Adventure modules happening against the backdrop of war and intrigue raging across the Flanaess would follow. Most of the "location based adventures", which don't really change over time, like the Tomb of Horrors or Castle Greyhawk, would be set in 576 as a default, but could be plugged in just about anytime. Others might or might not be timeframe-specific, depending (and if they are, I'd want to include guidelines for moving any of them around in the timeline).
And later on, of course, I'd want to start expanding the descriptions of the world beyond the Flanaess.