Actually looking through the list of Greyhawk adventures past, most of them seem to be silly spoofs. The only so-far unrepublished adventure worthy of the name "classic" (and having the grimdark tone WotC are trying to associate with Greyhawk) I can find is the Slavelords sequence (A1-4). But that could easily be made setting agnostic for a broader appeal.
Silly spoof and dark pulp are both a legit part of the campy feel of old Sword & Sorcery fiction, which D&D was going for originally. Sure, any adventure can be put in any setting, that's D&D too. Classic Greyhawk modules that have not been republished for 5E:
-Against the Cult of the Reptile God
-The City of Skulls
-Descent into the Depths of the Earth
-Dwellers of the Forbidden City
-Expedition to the Barrier Peaks
-The Forgotten Temple of Tharizdun
-The Ghost Tower of Inverness
-The Lost Caverns of Tsojcanth
-Mordenkainen's Fantastic Adventure
-Queen of the Demonweb Pits
-The Secret of Bone Hill
-The Temple of Elemental Evil
-Tomb of the Lizard King
-Vault of the Drow
-The Village of Hommlet
I would expect any of those to be potentially part of any future book along the liens of Saltmarsh or Yawning Portal. Sure, they can all be put into other settings, and only the 2E City of Skulls really makes use of any sort of Greyhawk specific metaplot (2E, ya know?). This isn't even getting into any 3.x era modules that people loved.