ENWorld by Beth Rimmels. And there's an excellent post by NewbieDM with pictures. I'm sure you've read the contents and seen the maps. I'm stoked, you're stoked. Here is my observations:
First off, the word going around from the Wizards staff is that Saltmarsh will be considered a "setting" and Greyhawk won't for purposes of DMsGuild content creation. Think about that for a second. Had they said sure, writers you can do Sword Coast but not the rest of Forgotten Realms then there would be grumbling, Barovia but not the rest of Ravenloft, grumbling. Sharn but not the rest of Eberron, grumbling. Why should Greyhawk fans be any less offended then? That said it's smart, because as I've analyzed before, the adaptation of Greyhawk classics in 5E is coming up to a crossroads. It will soon have to delve into actual Greyhawk story lines before long or be forced to switch to another classic setting like Dragonlance or Planescape. Futhermore, Saltmarsh was never an integral part of the World of Greyhawk yet it attained this classic status despite being canonically invisible. So, good on Saltmarsh as the choice for a setting to develop on its own. I take it as a sign Wizards knows its burning through IP too fast and is pumping the brakes.
Even so, from the photos shown in NewbieDM's post, we see Keoland, the Sea Princes and King Skotti are mentioned. This is fantastic exposure. The SW of the Flanaess is a popular area with a wealth of history and much open sea to explore. I should know, I've spent the last several years developing the Sea Princes and South Seas. Those DMs looking to start a high seas campaign in Greyhawk, check out my map HERE.
There is mention made in the pictures of at least THREE Greyhawk deities, one of which, Procan is entirely appropriate since he is the god of the seas. This is notable because Procan is not listed in the scant section of Greyhawk gods in the 5E PHB. I can only hope fellow nautical deities Xerbo and Osprem sneak into this module as well.
I've ran Sinister Secret of Saltmarsh before, it's wonderful, but not the other constituent modules (a couple which are Dungeon Magazine classics). I'm sure this book along with the rules section on seafaring will be amazing. I wish it had come out three or four books ago! So yes, I cannot wait to get this book. I also cannot wait for Greyhawk to be turned loose for real on DMsGuild. Until then, enjoy the Saltmarsh "setting".