I'm all in for this, although the developers got a lot of something else to do on their hands. :P
For the Chaos empire, the player sees how they rose to power, how they got their land, and how they imprisoned the Elementals before the setting of the Order Empire Campaign. They fight against some Order, some Chaos, and more of Elementals.
For the Elemental Empire, the player will help regrow their race after the Order has freed them from their cells (in the credits picture - after beating the last mission for Order Campaign - look carefully in the top-right and left corner,) and fight against more or less of Chaos, Order, and a little bit of Elementals.