The gameplay has been changed for co-op, which Oguro says was a requested feature of the first game. Some shots MTV took of the trailer show what appears to be a game designed for three players. In one shot they have three soldiers staging an assault together.
And in the sequence that follows, we see a mech get boarded by the three soldiers and commence a three-barrelled assault. Look carefully at the image and you should be able to make out the heads and shoulders of the three seated characters in the mech.