In essence 568 baseworld plus a 25 year timeline with possible events and adventures and how the 568 world changes. Then make suggestions for the adventures so that they fit with the new canon ' let the DMs guild add material based on suggested times and place.
Now this idea I really like. That would also be a very unique way of presenting a core D&D setting, setting it apart from other worlds, while also pleasing most of the fans of the setting. Play in any era with updated material for each era, effect change on the outcomes, rewrite the history, make Greyhawk your own. As I understand it, that was always the intent for the setting, giving you the rich backdrop that acts like a springboard to make the setting your own through your campaign.
I hope Mearls and Co. are reading this thread.