Brain in Jar Character from the first trailer Spoiler possibly.

[1minus1is0]

Here's another theory: The character in the teaser is having a dream/hallucination while being assimilated by the WAU. As he's dying, the WAU/structure gel is corrupting his mind, thusly why we see the room around him crumble away to reveal an body-like passageway. Maybe IRL raznik and nameless have structure gel enterign through their nose/ears/orifices and are dying.

Plausible, except when WAU gets to your organic body, you NEVER die. It's a core principle of SOMA.