Yet everything in the trailer points to what going on as not Covenant. We know about when the Covies attacked, and how it went down. There's no way to explain how there's no visible Covie ships, explosions on the planet (plus the fires in spots where there are no explosions), no Plasma bombardments, and an accurate Slipspace jump past the defense platforms which wasn't possible for either side pre-first strike, so unless the trailer is bat shit bullshit, I'm leaning towards a Forerunner, Precursor, or a new faction we haven't heard about. My best bet is Forerunner, seeing as the explosions on the surface could be some kind of defense system, which also resulted in something using forerunner tech to do the accurate slipspace jump.