I’ll keep this brief, apologies if this “theory” has already been discussed.
As we all know, Halo trailers are steeped in symbolism, often subtly referencing features that will exist in the final game. With that in mind, there are a couple of things that stick out for me from the last two Halo infinite trailers that I feel could be hinting at a major gameplay mechanic:
1.) The presence of multiple Forerunner “lighthouses” in the 2018 trailer - I think these will play a major part in the game. I believe these will act like outposts in Inifinite’s fully or semi open-world. I see these behaving much like Zelda Breath of the Wild’s Sheikah shrines or towers, with players traveling between them in a free-form fashion.
2.) “The Weapon containment system” chip - With the above, I think this will be the backbone of the game’s central game mechanic, my theory being that it will be the chief’s mission to contain Contana within this chip. The way he/we will do this is by traveling to each of the “lighthouses” mentioned above (along with other installation locations) and after fighting through to the center (which we see at the end of the 2019 trailer), he will contain a “fragment” of Cortana in this chip.
As the chief collects more of these Cortana fragments, perhaps it gives him/us more access or control over the Halo ring/ forerunner tech - perhaps opening up the map, or giving access to restricted areas. To use the Zelda metaphor again, perhaps Cortana controlled forerunner tech is the equivalent of Sheikah technology, with the chip being the Sheikah slate, the more Cortana fragments you acquire, the more you progress in the game.
I am a huge fan of Zelda BOTW so perhaps this is very wishful thinking - would love to know what you guys think.