About topic #4, maps are not infinite in size, and except for the first aren't usually expanded a whole lot, at least not under any current designs. It's possibly to add maps that are dynamically expanded much more broadly, as you can see in the Scrapyard, though it wouldn't serve much of a purposes besides fluff, either, so it's not worth adding.
Also, the engineers have a plan for what they're doing--it's not random.
Hmm, random wasn't quite the right word, more, I meant I wasn't sure if they were "merely" continuing construction of areas already marked by the map generator, like a Dwarf Fortress game with way too much pre-planning, or if they were applying their building rules on the fly.
Given that the core dungeon dosen't stay damaged or dug out, I guess you probably wouldn't be able to tell the difference, really.
The first method would let you just generate a more dense map than needed and turn off a percentage of rooms for live construction later.
I will say in my first hour of play in the new version, I found a secret door via terminal hack that lead away from the hallway the room was on, and when I took it, the room it connected to was still being dug and finished off of some other hallway. That was pretty cool.
That's one of the big things that's missing in terms of the ecosystem, machines being repairable or buildable, though these features were never intended to be added, either. Maybe one day (but probably not). Would be a neat bit of fluff.
Could also allow for the reintroduction of an occasional repaired/new interactive machine greeting when they have to run back through a area.
Also I sort of imagine the player observing a hubbub of robots, realizing that the engineering truckbots are carrying e.g. fabricator blocks, and trying to hang around out of sight to use the new toy when they build it.