What I enjoy about the survival genre is the tension produced by scarce resources and immediate dangers, but this is kind of self-limiting. If the player is able to progress at all, this scarcity and danger will abate, and interest has to come from somewhere else.
Different survival-type games I've played solve this endgame problem in different ways. NEO Scavenger acquires a plot with supernatural elements. Minecraft becomes a sandbox block building game. Resources are still limited but by no means actually scarce. Other games become entirely about combat.
What follows is a proposal how to keep a survival-type game interesting beyond the immediate "I have trousers and food now" stage with less of a shift in gameplay.
Willpower
In nearly all computer games, your avatar or units have infinite willpower and obedience. A few marines in Starcraft will gleefully charge a whole army of Hydralisks, getting torn to shreds in seconds. And your avatar in NEO Scavenger or Minecraft never despairs. As long as you are fed and rested and healthy, you can keep going, no matter the exertion. A bed in a tiny cave in the soil is just as good as one in a beautifully appointed master bedroom. Your clothes always fit and never chafe.
Now contrast that with a realistic assessment of what would happen if you got stranded on a remote island. Apart from the need for nourishment and shelter, you would have to deal with the psychological stress of being alone and the hardships of mere survival. You may end up having to paint a face on a volleyball just to stay sane.
Game mechanic one is willpower: It's a resource that recharges with good rest, good food, good clothes and the experience of beauty. You can use up willpower to temporarily boost your abilities: carrying more, moving faster, working harder. It allows you to keep going when you are tired, or ill, or in pain. You can function with zero willpower left, but it is tedious, dangerous business. You start the game with quite a bit of willpower in the bank, so it's not your most immediate concern. You can spend it to smooth out the bumps when you are doing your best to not die immediately. In the long term, though, replenishing your willpower becomes important.
Experience
Another issue with lots of survival games is that variety is kind of irrelevant. One foodstuff is as good as the next, and your avatar is fine with staying in the same place forever. For the player, discovering new stuff is part of the fun: a new plant, an interesting new landscape, a new item to craft, a different kind of shelter. But because of the mechanics of survival, going exploring is discouraged: you are safer staying in a place where you know the dangers, the food sources, the shelters. The game's rewards structure hence works against the player's desires.
To bring these two in line, game mechanic two is experience points that are gained only from having new experiences. Killing stuff does not gain you XP, nor does crafting or mining. XP is gained by seeing new things (plants, animals, landscapes, artefacts, books) and experiencing them directly: different food, drink, clothes, steeds to ride, and so on. This XP can then be spent on new skills, abilities, crafting recipes.
Together with the willpower mechanic, this should provide in-game rewards for extended play that includes exploration, experimentation, and working to move from mere survival to thriving comfort.
A Prototype
I might code up a really stripped-down prototype for showing off these two mechanics in a simple survival game. The prototype would track hunger, thirst, health, willpower, and XP. You would have to find food, water, clothes and shelter, all of which available in both aedequate and willpower-boosting variants. And you'd start out with zero crafting recipes, but could "buy" recipes with XP.
