Adding extra health requirements and dangers for the player in hardcore mode(s)!
You could add 2000 calorie diet/day requirement for the player. This one may be a little ridiculous, but it could be something to add.
Either that or a certain amount of vitamins/minerals the player would have to consume in order to sprint longer or regenerate heath perhaps?
You could make the player's body more sensitive to temperature, therefore the player could get hyperthermia more easily. Another addition would be adding temperature drop in caves that could make the challenge even more intense? You could also add frostbite, perhaps?
OR, you could make it so that the more stable the player's vitamins/minerals are, the less sensitive their body will be to temperature and/or other heath-draining sicknesses?
I know that illnesses and disease is on the Trello roadmap, but these are more of a perspective on what you could add to make harder gameplay optional(I recommend making it optional).
The more ideas I come up with, I'll add to this thread 
If you wanna go sims, you can have it where the player can actually eat too much, and you can finally make the toilet useful rather than just for looks 
And as always, red51 and KingGenius your hard work and dedication to this game is greatly appreciated!
