Speaking as someone who has just about every GH-related item ever released (with the lamentable exception of some of the early Minifigs, which I'm still trying to track down, having seen them advertised in early issues of The Dragon, and the LG material, which I intentionally eschewed), and who has dutifully kept up with all the releases and modules and books and boxed sets and so on and so on and so on, and who has been running Greyhawk since the original folio came out in 1980...
I wish they'd just let GH go.
Sure, I'll buy the upcoming book. I'm a collector. And I like Erik's work and know him to be a true devotee of the setting, ever since I was his DM back in Boston. If anyone won't make a pig's ear out of this, Erik won't.
But honestly, the more stuff that gets published just takes the setting further and further away from the original intent and feel. Part of it has to do with the changes in the game system. I went to 2nd Edition, but went back to AD&D 1E when 3.x hit. Not to turn this into yet another edition-war thread, but there really is a difference in the feel of the game. Greyhawk is embedded in the older version of the game. It derives much of its charm, its feel, and its nature from the older style of game-play wherein stereotypical heroes battle stereotypical bad-guys. Where archetypes battle archetypes, obviously and deliciously derived from the good old days of tabletop wargaming. Where encounters aren't necessarily "level balanced" or whatever you call it nowadays.
I say the less GH material that's published, the less chance that the setting will be screwed up any more than it already has been, by folks who want to set their own stamp upon it. I don't believe Erik will do that, because he loves the old Greyhawk that I do. But if they do decide to revive the setting as one of their core product lines, I shudder to think what new manner of nonsense will be introduced, with the ultimate effect of genericizing the setting to the point where it is indistinguishable from Eberon or the Realms.
Leave it alone, sez I. I'm willing to risk missing a single wonderful product for fear of enduring a dozen clunkers that ruin the setting.