Perhaps the only way a new Greyhawk Campaign book will satisify every group of fans is to make it a legacy item. No, not that kind.
I'm thinking of a book that tells the history of "Greyhawk the Setting", while also referencing all the eras with updated rules. For example, begin with the 1980 & 83 gazetteers, include the early Dragon articles, maybe pieces from the early GH modules. Then progress on to post 576CY WARS and 2nd Edition materials. Finally end with the new Living RPGA materials (including some from members' own material too).
It wouldn't be that radically different from most CS books. Just think in terms of mechanics; mark off each portion of any entry under an era or two. Region and History chapters could have strong demarcations. New rules and updates could easily reference NPCs, lands, and creatures from all played history (576-600?) or even before.
Wizards, if they do any GHCS at all, isn't going to publish era books like Weiss is currently doing for Dragonlance. What they do have to their advantage is the majority of older materials already in text. Half of that stuff has become D&D nostalgia. Heck, even the old maps could just be shrunk down to show multiple eras of play.
Lastly, and I have to say this just as an incentive, they could price the damn thing out at 75$ and wrap it up like the 30 years of D&D coffeetable book they put out. Crazy GH lovers will pick it up no matter the cost. (meaning: if you can't sell it as a supplement, sell it for what you can)