A noble effort, but GH has a big problem to keep that from ever occuring (and St. Cuthbert Knows I'd LOVE to see GH get a book ala the FRCS).
To paraphrase Elrond from the FotR movie:
"Greyhawkers are scattered, divided, leaderless.."
The fan base is carved out into too many slices..
You've got the fans who only like the 1E GH stuff when Gary was at the helm, and despise everything else
You've got a smaller slice that like anything pre 2E GH (including latter 1E stuff like the CoGH, FoI, etc), but 2E turned them off of D&D period.
You've got a small portion who like the From the Ashes Era stuff (and thought pre FtA GH was boring)
You've got a portion who likes the changes brought back by the GH revival in '98
You've got those who like all aspects of GH
And you've got those who know nothing of GH but the RPGA LGH campaign
I could sub-divide further.....
The most vocal "slices" are the Gygax era, and the GH 98'/LGG era..these are the groups who would buy the "RIGHT" product. But they can't agree on what the "right" product is. Perhpas if a compromise could be reached sales between the two slices would allow for a GH Hardcover. But catering to one or the other won't bring in the bucks WOTC needs to see.
Supporting Living GH is an option for some, but IMO the RPGA is just doing the living City junk over w/ GH names. Same as what has been done w/ GH as the "core" setting for 3E. Some folks say "you have plenty of GH support, it's the CORE setting". In actuality the setting has only been paid lip-service since 3E "revivial" other than the LGJ. Historically the setting si ignored, and WOTC just tacks on some GH names to generic Prestige classes, spel;s, and whatnot. That is not support in my book..
And this brings up another division among GH fans regardless of "Era of PLay":
Should we even HAVE detailed supplements about GH as a campaign world (non mechanics-wise). There are many GH fans who would love to see detailed books on different aspects of GH. Then again, there are many GH fans who want GH to be as little detailed as possible as it allows them to customize to their own whims w/out contradiction from the publisher (the way Gary meant the setting to be).
Personally I like all Eras of play, and I'd love to see a true Greyhawk Hardcover ala the FRCS instead of the horse-hockey that's been labled as GH content for the past 3 years (other than the LGG and LGJ) by WOTC, but unless the license is farmed out ala Ravenloft, DragonLance, etc, I don't see it happening. As another poster alluded to, GH has an identity problem, and the fans in the different camps further those identity problems.