Ive said before I think it will have something to do with the faceless. I also believe it will have quads. I don't see it being in west underrail, and while something like "hexagon only" is possible and would be neat; I doubt he wants to do a DLC anywhere in north underrail if the 2nd game is going to be there.
IF there will be a 2nd one.
There are some storylines that would be possible :
CONTAINS SPOILERS!
1.
You play as the agent that has been hired to infiltrate the faceless capital.
You spawn at the base of the oculites and your story is kinda connected to underrail, but during the time where the deep south (Not the confederation, i mean Junkyard and SGS) is blocked off from the rest of underrail.
The end will be : You delivering the cube to the Bakers, (Cuz they were in CC/RC during the time SGS was blocked of.) and telling Azif that it is done. You are free to go. And the game ends. The ending slides will be the aftermath of the theft of the cube, the Bakers fate + critical encounters that change the ending slides.
That was my 1. theory.
2. You are playing the PS CEO (Archibald) during the CC riots. You fight with the CT CEO and his troops against BioCorp etc. and the ending will be you retirering as the CEO of PS.
Endingslides could be the upcomming events like the murder of your son, the invasion of the faceless etc.
3. You are a protectorate Corperal. You'll find out pretty quickly why you were promoted to that rank etc. you'll be doing solo missions against the drones or other stuff, till you manage to do something big.
Then the end could come, you are being promoted to a commanding position, like the the protectorate boss, which is commanding the fort in south Underrail.
There are many more possibilities. It might play out before the action of the main game, during it, or after it.
-Azura