Rodan is a monster I have a sneaky suspicion might be in the movie. There were hints of him in the most recent trailer, or at least A flying monster. But from what I saw, it seemed very pterosaur like.
So due to popular comment, the next will be Anguirus. I was gonna do Ghidorah, but now I've got a few others in mind.
Oh, and the flying kaiju in the trailer is a Muto.
I have my doubts that the flying monster is Rodan (which I certainly hope I'm wrong). I thinks its a male Muto, as there will presumably be a Queen and male ants are born with wings.
However, if a Toho monster is in the film, I think Rodan would be the obvious choice.