I think it would be really cool to have the ability to change game attributes so it can be as easy or difficult as you want. On top of the developer intended settings you could add a "Custom" mode that allows you to toggle on or off certain things and have sliders for different scalable settings. Some very rough ideas include:
Debt multiplier - Possible range can be from a 0.25x - 5x (easier - harder)
Loot Value Multiplier - 0.25x - 5x (harder - easier)
Check boxes where you can enable or disable map modifiers. Default would have them all on or you can turn off any combination you want or even all OFF.
Check boxes to enable or disable entity spawns. I don't know if you could spawn enemies on maps they aren't usually on such as the soldier being on metro. Could be a cool none the less.
Sliders you could speed up or slow down entity spawns. (Instant to severe delay)
Options to change prices of things (Free items and travel - 5x prices)
Options to change item charges. (Infinite down to single use)
I'm sure there are more things that could be changed that makes the game more difficult or much easier. Giving the players the ability to play the game how they want could open so much replay value through challenge runs or just changing things up. All stats, xp gain, and achievements should be disabled during custom playthrough or at least if the game is made easier.