I'm not 100% sure about the story but I have a concept. The game should start with an execution from the army. The main char gets hit from a bullet in his chest. Of course he will survive and wake up with all the dead friends beside him. Now he can try to survive in the open world with lots of mountains and hills. He can either start to fight against the soldiers and try to find out what the army tries to hide or he avoid the patrols and just survive somehow. But if the soldiers see him, he have to escape or die. I think about hardcore mode, which will delete the savegame when the player dies. The soldiers aren't the only danger, other survivors(AI) are hunted by the army, too. They can either be friendly and work with the player or they try to kill or rob the player. The animals can also be an enemy.
Map -> Legacy Map(A Map created from me), Procedural Map(You can set the presets and the game will create the map)
Enemys -> Soldiers, patrol helicopter, animals, other survivors
Friends -> Other survivors
Locations -> Loot locations(Small towns or buildings), camps from survivors, roads, rails, harbor, trains station, ...
Building -> Foundations, pillars, floors, different walls with snapping to build your own house
Atmosphere -> calm and quite but sometimes really exciting and dramatic
Style -> First person open world survival game with realistic graphics but not to bright, it maybe should be a bit dark
I'm not sure where the game plays, maybe in russia.
I hope this answer is enough for you :)