: Saw this from redditor aDineSupremecist and thought it was a pretty
: interesting idea and wanted HBO's take on it: After Halo 5, let's rewatch
: the reveal trailer. We find out that this trailer is not exactly for any
: particular game, but for Halo in general on Xbox One. source

: So let's analyze the trailer: Considering the cracked visor, we know this
: trailer takes place after Chief's fight with Locke. We also see no Blue
: Team, who have been at Chief's side throughout Halo 5. Plus he's wearing
: that cloak, which is absent from Halo 5. My guess is that he's possibly
: hiding from them, or even the Infinity. Maybe they're dead, and he's still
: hiding for reasons unknown. Maybe everybody believes they can't trust him
: so he has to go on this journey alone, without being discovered, or
: risking the lives of his few remaining friends.

: So we then see Chief approach the Guardian. Notice something odd about it?
: It's lights are not blue like the ones Cortana controls, it's red/orange.
: The only other time we ever see this color scheme is when the Ur-Didact is
: in control of Forerunner tech. Chief grasps Cortana's former data crystal
: chip, and that's pretty much the trailer.

: Based on this information, I'm willing to bet that this does in fact takes
: place after Halo 5. But what other information can we gather on Halo
: 6/future games? Well we do know that the Ur-Didact is not dead, but was
: composed on Installation 03.

: We also know that there is a Forerunner Builder alive on Genesis during the
: events of Halo 5, though we never seen him and do not know his fate. We do
: know he was looking for the Bastion, a planet-sized Forerunner
: installation capable of moving through slipspace. He however couldn't find
: it and was trapped on Genesis. Plus there's the issue that Forerunners are
: still in fact alive, and the Builder most likely came from them. One
: Forerunner,

: Within a year after the events of Halo 5, Elites are hunting down Brutes.
: Whether or not this date will be retconned, for the moment we can say that
: Cortana is defeated sometime in the next year.

: The Infinity is on the run from Cortana, and the Covenant have been defeated.

: Speculation

: The Bastion that the Builder is looking for is in fact the Dyson Sphere
: (Trevelyan). It is too big of a structure (2AU in diameter) to not be of
: some importance to the Forerunners and the franchise. Seriously, a 2AU
: diameter is MASSIVE. Can anybody even do the math on how many Requiems,
: Halo Rings, Arks, etc could fit into that? The Builder said that it would
: be near impossible to take it out of slipspace, but it was moved. My guess
: is that the Sentinels stationed at Onyx move the station when it's
: location is comprimised, and set up a new "planet" elsewhere
: with the station in the same slipspace coordinates. This way you couldn't
: find it in slispace, but would have to find Onyx itself as it was the key.
: For all we know Trevelyan has a huge Forerunner population in stasis
: inside of it. Considering it's size, I wouldn't be surprised if the UNSC
: hadn't found them in the 5 or so years they've been stationed on it. He
: may even be forced to fight against Cortana.

: Now you have the Ur-Didact. I'm guessing he controls the Guardian in the Halo
: 5 trailer. Maybe he and Chief need to join forces to take down Cortana? My
: guess is that he moved his consciousness from the isntallation into the
: Guardian, and hoped to use it against the humans. But Cortana couldn't
: take control of it since he was in it, hence why it's not blue.

: Who knows on Guilty Spark. Maybe the Infinity will run into him for all we
: know. Maybe they'll flee to Trevelyan. Anything is up to grabs on those
: two groups.

: We also know that the Flood may have their main forces outside the Milky Way,
: and may come back someday. Plus the Primordial become the Flood, so he may
: have split part of himself off to go find the main forces for revenge at a
: later date.

: TL;DR The Forerunners are going to war with Cortana.

: - MacGyver10

Hmm, considering Cortana controls machines meant to single handedly control an entire planet she would be a formidable foe. Having actual forerunners helping the resistance (that's what I'm going to call all the forces fighting Cortana) could help even the odds. Also, a very common motif among 343i is the expansion of forerunner lore and importance. With Bungie, forerunners were just this long dead race with really cool toys, but 343i is really trying to humanize them and make them a separate faction in the Halo universe. It'd really cool to fight and talk with living, breathing forerunners and it would give them an excuse to greatly expand the forerunner weapon/vehicle toy box. However, I'm going to take this with a small grain of salt because this is mostly based on the assumption that the Bastion is the Onyx dyson sphere. Argument is compelling and it would be cool.