We're still wondering how Greyhawk is relevant. Let's look at it from a different perspective - ease of use by a new player or DM who doesn't have the tribal knowledge needed of other campaign settings.
Greyhawk is relevant because a DM can take either the WoG boxed set or the LGG and use it as-is as campaign setting without having to deal with any metaplot problems. More importantly, unlike Forgotten Realms, there haven't been more than one world-shattering event. We had, in recent in-game history, one - one event - a world war, which is very easy to ignore. You can go pre-war, or you can go post-war. No worrying about the deities walking the earth and multiple iterations of the same (Bane, Iyachtu Xvim, back to Bane, Orcus/Tenebrous/Kiaransalee, etc.), no worrying about spell plagues.
For the players and DMs getting into D&D for the first time, that is way too much backstory, history, and metaplot to try and digest, especially since it is much more detailed than Greyhawk.
I think that if Greyhawk were to be re-issued, they would need to go the Goodman Games "Known Realms" treatment - a big boxed set and then pretty much hands-off other than tidbits within the adventure modules, or the FRCS route - one big book, but then hands-off. Golarion is being handled fairly well, but they have the horsepower to produce quality supplements adding detail to various locales.
Looking at the Gazetteer of the Known Realms, each realm averages maybe two pages, tops, for each entry - and they are just detailed enough to set visions dancing in both player's and DM's heads alike - and that's all the info the player's should be getting (recent history, various settlements, rulers, population, power centers/factions.) The DM's guide goes into some detail about ancient history/creation myths (with no crunch) and then details the pantheon, world-specific monsters, feats, classes, equipment, and spells - stuff that the DM can choose (or not) to expose to his players. The details of each of the various significant NPCs (rulers, famous heroes/villains, etc.) are very limited (for example, the leader of the "main" dwarven kingdom is really not much detailed than his name - he is described as "LG male dwarf Ari3/Ftr14, Str 16, Con 17, Wis 15, Cha 14, along with some text about his motivations) That's it. No detailed list of spells, feats, or magic items he carries. No long drawn-out history of his achievements and how uber he is. This fits with the old-school feel sought by the DCC line. It is that feel that makes Greyhawk feel "right." Limited details, providing DMs and players the framework to provided a populated world that they can go and conquer.
Seriously - the way to properly support Greyhawk is to clean up inconsistencies, clarify canon, and then allow DMs and players to expand upon it as they see fit within their own campaigns. No metaplots, no one-pager descriptions of NPCs, No having to track through a convoluted history. If *any* metaplot is desired, it ought to be done only in the way that (go ahead and groan now) they attempted to do in the TORG game - individual DMs provide feedback to the company and the majority outcomes of various strategic plot points becomes the "official" canon moving forward into the next products. No novels driving the metaplot. No deltas between various novels, no arbitrary changes to the campaign world that the players and DMs didn't at least have an opportunity to affect.