In a post on the official Xbox blog, GSC Game World has given a bit of description to that in-engine teaser trailer from early January. Stalker 2's protagonist is Skif, whose eyes we see through in the teaser video. That's the character's Stalker name, remember, as Stalkers don't use their real names. (They are criminals, after all.) According to GSC's post, Skif's actions "will shape the new grand chapter in the history of the Zone."
Perhaps most satisfyingly for me, the trailer scene is confirmed to take place in the ruined elementary school on the outskirts of Pripyat, which is where I guessed it was at the time. The loud, roaring noise outside during the trailer is confirmed by GSC to be an emission, the blasts of energy from the center of the Zone that mean Stalkers have to take cover indoors or face gruesome consequences. (Death, the consequences are death.) That's why Skif is in a hurry in the trailer: He needs cover from the emission ASAP.
Finally, the guitar tune is pointed out to be Life Line, by "famous Russian rock band Splean." Neat.
GSC also says development is "progressing smoothly," confirming RTX support and 4k resolution on the Xbox Series X—something you can safely assume will also come to PC. They're still not ready to give a release date.