Instead of having hit points, have a system which models the basics of the human body. The human body does not have hit points, it has bones, flesh and blood. The long term goal here would be a major step towards realism, along with a major change in the way mutations are figured. Instead of has8legs〓true, you end up with legs 〓8 when the player acquires such a mutation. The same would hold for other body parts. If legs> 2, you cannot wear pants. If a creature has no eyes, it doesn’t see. Limbs could be destroyed/removed/mutated, and added through bionic replacements, or possibly clone parts.
The inspiration is from Dwarf Fortress, which has a system like this. Cataclysm dda seems to model a larger number of bodies than df, so less detail would probably work better. I can think of dozens of ways that a change like this could make for new challenges, tactics, item niches and character development.
Cataclysm is a game that doesn’t just tell a story, it makes up a new story every time you play. I have had characters taking off their pants in the back of a liquor store, cutting them into rags and constructing molotovs while a horde of z’s pounds down the front door. You just can’t write things like that. You create the world, and let the stories unfold.