From what I hope to guess, that is Master Chief on the trailer. Not reason it should be someone else. However, for some reason I think he also had a visual change besides the old classic Halo style in return.
Back in Halo CE-5, He wore different types of armor visually. In the new trailer his armor seems… More linear. Like as if he took some of his armor off. In a way that could definitely time or stress of a situation. Like back in from Gears 2-3 on how they changed. Maybe now Chief is getting a new visual rework from clunky armor to light armor and more robes and straps.