Judging from the two trailers, and from Hack Fraud saying its about environmentalism, its probably a game about the metaphysical significance of oil taking a literal form. The skeleton soldiers are resurrected from WWII, one of the first wars with large motivations on oil (especially in the Pacific Front) but are supported by a more modern soldier (and living) through umbilical cords, which recede back into his gear (likely his stomach) Reedus has a scar in his stomach, and will likely share the power with that soldier of being able to control things with them.
Some other details I noticed
We see Reedus's hands are covered in oil, then when it cuts to the first person shot we see smaller, baby sized hands making oil prints in the sand. Likely supposed to be symbolic of how mankind influences the environment with his every action
Reedus is covered in grime, yet has uncovered handprints all over his body
When the doll touches Del Toro, a few cords grab it around the leg and slowly pull it into the sewer
The army and soldiers are clearly on a manhunt for Del Toro, who is fleeing with a fetus in a device. Perhaps the reason resurrected soldiers are used are because there is a shortage of actual humans. Perhaps overexposure to the oil and its powers killed all the women/made them sterile and only remaining humans are rare but now exert great power of things powered by oil
When the soldiers march across the bridge, oil leaks down its side
Del Toro is wearing a handcuff on one hand just like Reedus. Using camera framing, this detail isn't very noticable until the end of Del Toro's presence in the trailer
The baby doll has cuts in its stomach like Reedus.
The Bowie looking guy manifests in a red fiery sort of effect. Looking back on the first trailer, when Reedus is looking up at the floating guys one the left and right side of the screen that fire effect is manifesting near the ground
Baby dolls are made from plastic, a product of oil, and all of the dead soldiers presumable without oil powers are using weaponry that doesn't use plastics in it, but the living soldier is using equipment with plastic. Perhaps this implies the oil powers allow you to manifest products of oil at will? Maybe at some point they attempted to create a surrogate human with oil powers and failed, making real humans even more valuable? We see the soldier make his helmet disappear in that fiery effect
The necklace Reedus is wearing has equations on it, and notably again appears to be constructed from metal. Perhaps those physical equations are incredibly valuable, hence being carved on materials not able to be influenced by the oil powers.
Then there is the most interesting part, at the same time in each trailer the baby disappears from Reedus and appears for Del Toro
So my conclusion, how will it play? I heard somewhere that its supposed to have multiplayer like Dark Souls, so I'm guessing given all the other symbolism there will be a "souls" counter except for oil and its powers, you can invade other players taking a form similar to the Bowie character. If it truly is using the Infamous Second Son engine, than there will probably be an emphasis more on your oil powers than gunplay. The world will have, as part of its mechanic, parallel realities, both because Kojima will use the opportunity to use his imagination, and because Kojima likes to dabble in the "meme magic" topics, probably some Mandela effect themes as well.
Basically, Kojima is trying to stay on the cutting edge of memetics, make proper innovations on Dark Souls multiplayer mechanics, address the concern of a limited supply of oil and the impact oil has on our life, and somehow incorporating horror/stealth into it.