: 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

While this is probably better thought out than what we'll get.... It has far to many holes. And it also assumes that the initial trailer was anything more than a teaser in the most basic sense. It's a shame, because I'd love to see Chief on a solo adventure in hiding and injured.. but given how co-op focused the franchise seems to want to be I doubt we'll ever get that.