Monsters that just happened to coincidentally look like the original ones? If it isn't Rodan, it's heavily inspired by him because I don't find it accidental that both creatures just happen to be species of pterosaurs in a Godzilla movie. The other one is a mystery, but you can't fault people for assuming Gigan. Creature with a hook for a hand/leg? In a Godzilla film? Screams Gigan, but the trailer only showed the hook & nothing else, so it's a strong possibility it's not.
Besides, with as well as they're teasing Godzilla & creating hype, they shouldn't have to act as if there's zero chance of other monsters from the past films. They've created so far, a proper image of Godzilla which leads me to at least believe they would create faithful images of the others. The only question is how well they would write them into the story, but I'm already curious to see how Godzilla himself is handled towards the end.