Sorry to necro, but in light of the rather momentous recent update, I've decided to revamp and re-release this mod! Any suggestions for new additions are welcome- mechanics, factions, creatures: anything you can think of, I'm open to it. Starting work on it now, hopefully I can get everything already in the previous version ported over to the new build by the end of tonight (though maybe that's being a little optimistic. We'll see.)
PTW, this looks great!
Have you messed with caverns? You could make them significantly more hostile, perhaps even a cavern dwelling race of formerly-humans who tried to escape from the worst of the wastes, only to suffer significant mutations from the previously mentioned wastes. I imagine random body parts missing (fingers, maybe a hand or a leg, chunks of flesh, etc...) and twisted broken skin with puss-like ooze secretions, tortured grim eyes and teeth that are mangled beyond recognition. The mutations could give them enhanced agility and reflexes as well however, which would increase their deadliness significantly if they're any good at dodging. Also maybe even radioactive/toxic blood with an ingestion symptom that causes the victim to go insane? Might be a bit of a stretch but hopefully you get something out of the ideas!
Edit: What I suggested sounds like trashjumpers from what you said in the OP, but I'm not sure if they're a cavern race not. Either way I didn't realize the similarities, my bad.
Edit 2: Along with them you could also turn the caverns into another wasteland with things like toxic sludge and super mutant creatures, but I would try to make it a little more !!fun!!. I'm not sure what direction you want your mod to go but creatures that are a little weird like the 40d tentacle monster almost seem a little fitting for some deep secrets in an apocalyptic shithole
it would certainly be a fun discovery to say the least.