I personally think that based on the fact that the first four races in  DOW 1 was SM, Ork, Eldar, and Chaos it is going to be that, and im hoping for it too cus i cant bare to wait for an expansion to have me some chaos.

I bet its gunna be tyranids as a non playable enemy race

It has to be the nids, why the heck would any other race do that sort of display. When the nids come to a new planet they block out the sky with all of the spores they launch...which is what that stuff at the end loooked like.

Probably right, just hoping they dont give my Chaos the shaft it would suck so hard. Maybe we can hope that their lying to us and have five races in DOW 2

im guessing nids

Four races in DoW II, and they are Space Marines, Orks, Eldar, and Tyranids. The discolored sky was obviously due to Tyranid spores, not a warp storm.

Be a hell of a way to introduce the Tyranids if they're the focus of the singleplayer campaign, especially since people kept clamouring for them in the original Dawn of War.