Honestly, I would prefer them to have default setting and an entirely new one at that.
I know, heresy and dumping all over the things of past and all that, but, really, how often can we retcon Greyhawk and other settings to fit them into new rules systems?
I would much rather see a setting that actually takes the game mechanics into account, which rules out GH and other settings.
OTOH, the actual GH content in 3e is pretty sparse in the core books. Besides god names, some proper nouns and a few odds an sods, there isn't much GH there, so, if that's the level of base setting that's proposed, then I'm pretty happy whatever the setting.