...I can't resist.
Monster X- I'd be very surprised if they kept him out. He's fairly popular with the Kaiju fandom after his role in Final Wars, and his humanoid stature would make him perfect for all kinds of kung-fu moves.
King Seesar- Like X, he's mad agile and could use a lot of creative, high-flying moves. That, and his Beam-Reflecting eyes would be interesting to use.
Dagarah- I realize he was never in a "Godzilla" movie exactly, but he's got a really cool ability list and he deserves a lot more than simply appearing in Rebirth of Mothra 2 *cringe*.
Hedorah- Give him all of this forms, all of his original abilities and they could really make a neat character with this guy.
Titanosaurus- From what I know, this guy and Hedorah already have very good chances of getting into the game, and for good reason. Titano was a sick physical brawler in Terror of Mechagodzilla, and his Cyclone Tail would be a cool long range attack.
Zilla- He earned some respect after his appearance in Final Wars, but Atari shouldn't stop there. They should make him the Cartoon version, where he had fire breath and was equally as strong as most of the real Godzillas. His burrowing, agility and speed would further make a really cool fighter.
Varan- This guy deserves more, dammit! He's been in one old movie and a couple of books, and that's it. He's got a sweet design as it is, and he could look really mean in Atari made him a bit slimmer and added some extra detail. He'd be perfect for savage brawling with all of those claws and spines, and his gliding ability could be implemented well.
I don't give a sh-t, I'm at least renting this game when it comes out. And if I can find the money, I'll probably buy it.