The theory that these AIs are being controlled by something bigger and badder is one i would agree with. If you watch the end of the trailer that deep ominous voice seems to obviously be the main threat. "I have long dreamt of this day, Reclaimer" He also refers to master chief as "reclaimer" just as Guilty Spark does. Could there be some sort of connection between the two? Or have we already identified the Ominous voice? It seemed to know Chief was on a collision course with Requiem, and has something planned for him.