Development went pretty far, considering some areas already had VFX and SFX added to them. The most interesting thing is that there are loot triggers placed around (there is no loot inside them, as expected), but the triggers themselves are there.
How would it have played out?
The map size was a square that was supposed to be 6 km × 6 km. We would travel to different areas (possibly cities like Tycho) using a special car. Sadly, we don't have a good-looking model of it. The only one that exists is made of basic shapes.
Considering that the moon colonies don't abide by Corpo laws, the DLC's main focus was most likely not Arasaka, although Militech could still have been a secondary antagonistic corporation.
We know there was supposed to be a boss fight, and there were characters named Kenji and his mentor. There was also a Corpo bunker we would have visited, and something related to the Mass Driver. There was a Militech prop car near it, and the Mass Driver itself looked damaged. We would also visit a Drug Lab and a school ( Atleast I think that was a school )
There is no way to know whether it was supposed to be open-world or linear.