Has the potential to be a pretty nice game
A few suggestions (some you might have in mind but didn't mention)
A depth counter - since the idea is to descend as far as pssible it'd be nice to see how many meters, feet, fathoms, whatever I've gone down.
Injuries system - Currently (early build I know) you can fall any distance with no harmful effects, since you are thinking of a needs system and medical items, I think this would tie in well. It would also tie in with the ropes, making you use them rather than just tossing yourself down the hole. Injuries could hinder the player too, slow movement down, reduce jump height, reduce field of vision, reduce number of items you could carry.
Underwater/Water - Flooded areas. When I see caver's on TV go underwater in a cave system it make me feel ill. Could be nice if you can work it into the generator.
That's all at the minute I'm sure more will come to mind later