Making it Greyhawk will make no new friends. Greyhawk is incredibly difficult to make, since it's got a lot of lore at different periods. It's another "Kitchen Sink" world, with not a whole lot new stuff to offer. Not to mention it's not got a "gimmick" to hang its hat on. And I'd wager that most of the Greyhawk fans are still sticking with 3e.
WotC, I feel, cannot win with making Greyhawk. They're not going to pull Greyhawk fans into 4e, and they're more than likely going to anger those that like the setting.