Brain in Jar Character from the first trailer Spoiler possibly.

[caffeine4671]

I thought the room in

Spoiler below!

Alpha with the WAU in the middle that can eat your hand was the same room as the end room of the teaser, personally. Just WAU has grown over that particular brain.

They are a little bit different though, no? At least from what I can tell.

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.