There isn’t another Kong film between this one and Godzilla Vs. Kong to do any of that heavy lifting, so it makes sense that there will be some stuff in King of Monsters to lay the foundation for the two halves of Legendary’s MonsterVerse to finally unite.
The Monarch organization will play a big role in King of Monsters, and Brie Larson and Tom Hiddleston’s characters from Kong: Skull Island were recruited by the organization in that film’s end-credits scene, so maybe their pictures are still laying around.
I imagine that we may hear mentions of Skull Island or the lost expedition of 1973.
So those looking for hints of King Kong will be likely to find them, but the movie isn’t going to hammer you over the head with the giant ape by the sound of it.