Some Interesting opportunities?....
nutritional deficiencies (scurvy, rickets),
infections (malaria, unclean wounds, influenza),
temporal diseases (if you get over a certain level of damage from a monster, esp. like the ones found deep down, there's a % chance you can develop a condition that's similar to rot or rust. This could be temporary, or it could be permanent but reversible.)
Their implementation would have to be limited, otherwise players would have a lot to keep up with on top of getting food, avoiding wild animal attacks, making shelter, mining, mitigating spoilage, etc., especially for players who love more extreme climates.
It could be fun if the devs thought, "So, I see some of you players want to live in a tropical climate where food has long growing seasons. Here, now there's risk of malaria to contend with." How to implement something like malaria though? I don't know