Also, as to that being a Cobra storm trooper, no. Just no. Let's go by this step by step and show why from what we can see from only seconds in the trailer.
First we see a panned out view, where Cobra Commander is standing on the exact middle of the walkway, overlooking everything, as Zartan walks up to stand to the left of him, with Firefly standing in a relaxed pose to his right as miscellaneous soldiers are in the background, dressed COMPLETELY different from Cobra Commander.
Then ti cuts to the side with side of Cobra Commander with Firefly, the camera showing Cobra Commander in the forefront and it angled down from him to firefly, which is a classic cinematic trick to show authority or power.
Then Cobra Commander tilts his head and it switches view to Cobra Commander presumably listening to Zartan who is talking.
Furthermore, let's look at his outfit, its a high quality material of a dark blue. He's got a faceplate with the rest of the helmet with details to make it look like a Cobra head, sort of a full headed version of IDW's original cobra commander design. Oh, and a red cobra symbol design on the helmet. He's also standing in the exact middle of the room and the two people seem to be deferring to him.
So, let's add up the facts. We have someone in a blue outfit and a silvered face-plated helmet, which in GI Joe only was on two things: Cobra Vipers or Cobra Commander, were it not for the outfit not being of a soldier. He seems like he's probably in charge due to positioning, cinematics, and common knowledge. Oh, and Zartan has taken over the USA (and probably world) and his boss is Cobra Commander.
TL;DR, he's probably cobra commander because he's got all of the iconic Cobra Commander elements and seems to be in control.