Just another idea involving the economy of the game.
Would be cool if the Underground had some sort of Casino where you
could gamble your money. Obviously, every game would have a house edge, so only games like Blackjack, Roulette, Craps, Baccarat, etc.
Obviously this can be easily exploited by save scumming, so maybe make this an Ironman Only feature if/when Ironman Mode is a thing? Then make it so the game automatically saves after each hand/roll/result.
Could also make it so if you're in debt, whether from gambling or loan sharks, the underground hunts/harasses you occasionally. Maybe they even find where you live and break your leg or something.