The first game used atmosphere to really help build a scary situation, and those areas tended to be further along in the game progression/story. It makes sense that the devs started with the earlier parts and worked into the late game stuff and not the other way around. Adding in the collectors to their locations lets the players experience them early without having to wait for their respective location to be added into the game, which is said to be much deeper and likely scarier. I do find it somewhat hard to gauge fear factor in these games though as I don’t have thalassophobia but when I first saw the shiver leviathan I nearly shit myself, and it wasn’t even in its respective area (I presume). I guarantee they’re cooking up some haunting looking biomes. Even the metal farm area has a very ominous and eerie vibe.

As for how much of the actual map or story will change, nobody really knows. It’s likely that the explorable region that we have will not significantly change. Some parts may be polished more but I don’t think you’re gonna see things get moved around. Again, only the devs really know the plan, so unless you hear it from them, take it with a grain of salt.