I've checked and it was semi-volumetric rendering of clouds that was removed. With regards to the fog, there seems to be conflicting information regarding what was originally meant to be in the game. I have heard some people talk about semi-volumetric fog and other talk about aerial perspective fog. I was referring to volumetric fog and PhysX as I know that Metro Last Light used PhysX to render real-time fog volumes. I think the problem here is a lack of communication as you mentioned. Hopefully there will be an Nvidia graphics breakdown when the game is released.
I don't remember seeing anything anywhere about volumetric fog, I believe stuff like the fog in the swamp was a dense variant of aerial perspective fog. Also, the semi-volumetric clouds appear to be still in the game, they are just dependent on weather conditions - which I know sounds bullshit, but is actually true. The closest thing to Metro's particles (if you were referring to this, apologies if I am mistaken) are the lit soft particles, which are not really rocket science. The thing is that none of the effects in the nvidia video are nvidia-exclusive effects. It seemed to me that this was more of a branded rendering breakdown. For example, screen-space reflexions aren't something that I can imagine being nvidia/gameworks.
I should clarify that I actually hope most of these aren't. Most gameworks effects are far, far from optimized and tend to tank the framerate hard.
Finally, I completely agree with you that at the end of the day, this is an issue of communication. I hope that we'll know more after release as you said.