Well, honestly, just fixing the AI would bring a hell of a lot to that direction (on top of improving the game experience and the balancing of the game. Two...No, three birds, one stone).
I mean, I would feel much more immersed if...
...Enemies were not throwing their grenade 50 feet away from where I'm standing (I'm not asking them to be pin point accurate every time and can be generous with the AI but if they could at least realize you're standing out of their throw range by a long shot, that would be a good start).
...Enemies, running around without knowing what they do, ending up in an entirely different place and looking for you because they forgot who was the person they were fighting (you know, that phenomenon at the end of pretty much every quest that ends up with the player wasting 15 minutes of his/her life looking for them accross the entire neigborhood with the Benny Hill music playing in their head....
....Enemies taking aggro but not reacting to you at all. They're just casually standing here shouting "catch the b***!" or the like (Are they cheering their friends?). Usually happens when they're far away because this game also has a huge issue with managing detection and combat (enemies can detect you but fail to go in combat mode) but that's a story for another day.
....Drivers actually brake when needed...Instead of just honking like a lunatic thinking it's gonna magically stop their car if they do it for long enough.
....Drivers were at least capable of driving around your car when you stop in the middle of the way....In fact, it would also do a lot to immersion if they could quit stopping in the middle of the road (preferably the highway) for no reason whatsoever (are their optics rebooting?).
Bonus round and fun fact: Bugs also affect immersion
-Making NPCs and cars spawning off screen, not right in front of the player, would also help a lot in term of immersion. It would also contribute in making the game experience better, as they can absolutely spawn right in front of you....Which is a problem while driving. I rolled a few citizens over like this, the game suddently spawned them under my wheels while the coast were clear a split second ago.
-Making cars, including yours after you call it in, stop in a normal way, with the braking effect and everything...Not just suddently freezing in place, like it happens sometimes.
Both lists could go on and on.
What I'm trying to point out here is that, before adding new immersion related stuffs (even if they're easy to include and/or their animation already exist in the game), it would be better if CDPR fix what is currently damaging the immersion to at lerast an acceptable level and then, they could start thinking about details and things to add.
Don't get me wrong, those ideas that are brought in this topic are great, they would indeed improve the immersion quiet a bit but in my opinion, CDPR should take one thing at a time, fix the AI/bugs because they also damage the immersion on top of the game experience and then, once it's done, start thinking about new features.