"Set in the aftermath of Halo 3, Master Chief returns to confront his own destiny and face an ancient evil that threatens the fate of the universe."
-official Halo 4 description.
Also, in an interview frankie said the the new trilogy would tie in past games, current games, current fiction, etc.
Hear me out. In the official description for Halo 4 it says "Master chief returns to confront his own destiny".
What if his destiny is tied to that of the forerunners. The didact and company?
100,000 years ago, after activating the Halo array, Didact and the surviving forerunner went on "the great journey". No one knows exactly what the great journey is, but what if for example it was something like the infinite meditation that didact was on early in Halo: Cryptum. Didcts cryptum, to be precise.
Chakas and Riser and bornstellar had to go through a series of puzzles and trials to open the cryptum. Didact imparted his memories upon bornstellar.
So imagine, Master chief lands inside this forerunner installation (which sounds a lot like a shield world). Inside he finds blue team along with halsey and co from GOO (remember, forerunner slipspace portal technology is far beyond humanities, just because blue team entered the sphere at onyx does not mean where they ended up was at onyx). From there they seek out a series of terminal like things. Master chief enters these and from them he is imparted with didacts memories, but the the memories are playable. You take control of didact as he fights the flood throughout the forerunner-flood war. This culminates with activation of the halos.
So master chief is then imparted with the knowledge of the diact and what he had to do to stop the flood. Lets say that for example "the prisoner" is still alive (hence the ancient evil). After receiving didacts last memory, John and blue team must put an end the the ancient evil. After doing so, they seek out didact and the other forerunner and awaken them from the great journey. The prisoner had been imprisoning them in their slumber, and the didact used the terminals to try and get his message across.
Didact then tells him that this was the plan all along. John has been imparted with all the knowledge of the didact, and in doing so has become the didact himself (his destiny). John, the remaining spartans and Halsey are all to take the mantle, all the forerunner technology and all the forerunner memories imparted in them and return home (to earth). They are to return and fix the broken galaxy (as it is in shambles after the covenant-flood-human war).
In summary, this trilogy could be about didact and the forerunners handing the mantle off to humanity, via the spartans, the ones they deem the most worthy. John becomes the didact. You can imagine that halsey for example would be imparted with the knowledge of the librarian and would take up that duty. In a sense John and co become like gods, who return home to fix the galaxy and set humanity on the path the becoming the galaxies protectors, like the forerunner once were.
So yeah, I HOPE you can make sense of all that convoluted mess I just wrote.
[Edited on 06.10.2011 12:00 PM PDT]