Looking at the two pictures side by side, the first (with the kneeling Sith). You can see the field littered with Republic commando corpses, one dead sith, and the kneeling (possibly about to be executed) sith. They are identified as sith because of their armor (look at previous CGI and videos) and the kneeling sith's lightsaber is just finishing deactivating (red glow on the ends).
In the second picture, it is from a slightly different angle, time lapsed just a tad. We see the dead Republic commandos again, 2 dead sith (the one kneeling is now face down behind the guard to the left) and a dead Jedi in the foreground.
The 2 standing guards do indeed look like clones, wearing identical armor and insignia, different colors. As was already deduced, this is likely the Knights of the Fallen Empire.
Frankly, i'm excited. The ending of Ziost showed me this was coming, and as has been stated by another user, simply killing the Emperor would end the story. I would feel ending it at this juncture would feel cheated, as the Emperor is supposed to be as powerful as he is. This is a good way to make it dynamic, fun, and engaging once more.
I'm so so SO very glad it's heading this direction with the story telling. It's why I was excited Bioware was doing this MMO in the first place. You guys are top notch when it comes to story telling, and having past experience in the TOR universe is a definite bonus. I look forward to getting through this adventure/story, and not feeling like it's another dailies grind.