From what Alessio said -
The Corporation - Human army, oppressors, intrigue, bribery, assasination, think East India Trading Company, expansion of the British Empire, Space Nazis. (His words)
Forgefathers - Elite space Dwarfs based on Norse mythology. Only race powerful enough to stand up to the Corporation.
Marauders - Space Orcs - The best shock troops (and mercenaries) in the galaxy. Trained from barbarians by the Corporation, but broke away (violently) and now work for themselves. The A-team of Warpath.
Rebs - Breakaway from the Corporation, plus a variety of non-human races. A rebel alliance, which may or may not involve psychic trickery and glow-in-the-dark swords. The entire cast of the Cantina bar. List will start mostly human (70%) but will look towards encompassing lots of aliens. Also, could be a testing ground for new unit types.
Zz'or - The hivelike alien menace - think Aliens, Nids, Zerg. Not approachable.
The Plague - Space Zombies - Alessio is more of a fan of slow zombies. Think Resi Evil, Dawn of the Dead. Plague causes nervous system damage most of the time, creating Zombie Hordes, although in rare cases it causes random mutations.
Asterians - Space Elves, but based very much on our concept of Grey Aliens. Superfast ships, turn up, take specimins, vanish. They have pointy ears.
The 8th Race - They said nothing. Except they will probably be the 4th released after Forgefathers and Marauders in the box, and the Corporation. Not Space fishmen.