I'm on the fence. Almost everything past Gygax's departure has been crap, both from TSR and WotC. Making Greyhawk the default in 3E was the death knell for the setting, since it turned into generic nothing. Because of this I'm pretty hesitant of Greyhawk getting a full revisit. Ghosts of Saltmarsh was really well done, at least the Greyhawk part of it, but that could be the exception, rather than the rule.
The big trick to new races is not upsetting the existing canon. For example, dropping a Dragonborn empire into either the existing setting or the history of the Flannaess would be nigh impossible to do without disrupting too much. Adding creatures/races is easy, so long as they aren't something that competes with the with "common" races. In my GH campaign Dragonborn are the equivalent of half-elves and half-orcs, being the descendants of of half-dragons. Goliaths came about in a similar fashion with giants.
For centuries they were an unknown shadowy organization, but then "first reports" of them occured 3 years prior to the start of the boxed set (CY 576). It's never stated what these reports are, allowing the DM to determine how they wanted to use them. I found them to be an excellent bogeyman, working as a shadow organization that even uses its own name to its advantage, such as getting someone accused of being a member. Their end goal was largely irrelevant, since success was nigh impossible within the timeframe of a campaign, making it about gaining power. Their public reveal was a terrible decision IMO.
