I apologize in advance for using google translate.
We have already skated on several levels of the metro, have been in the deepest caves, swam in jets on the underground sea, even accidentally looked at the base of the gray army.
But what about being able to surface? For example, in one of the abandoned laboratories of the biocorp or another corporation from the big six, there is an old abandoned elevator to a small base on the surface - the player, with the help of some faction, repairs the elevator, will be able to get there and make short and damn dangerous sorties.
It's like the black sea zone. Travel on the surface, because it is unsuitable for life and probably very toxic, it can be done only on special vehicles (to protect itself from the effects of the external environment) - for example, an isolated armored personnel carrier (with a closed life support system). To leave for research from an armored vehicle only in certain places ... otherwise, leaving the vehicle in a random place and without means of protection - health is quickly lost and turns into a mutant.
At the expense of the enemies, I do not even undertake to imagine who or what could have survived there. The turret on the transport could definitely help here.
Honestly, I bought a similar update without even thinking. This is Underrail! But I can't imagine how much effort and money it will take to develop such a thing ... most likely as much as the addition of the expedition.