I was thinking about the progression of the game as time goes on and if it will have more complex structures. I have an idea where a group of enough people come together they start a “clan” “guild” whatever and elect a leader or whatever. This person would have access to more complex structures or items for the group. Maybe a more complex RTS type overview (just of your base that you are in) of structures with the ability to place stuff. I am not sure how complex things can be made with the Unity Engine so I won’t go much further in depth if this is just a waste of time.
Another idea would be the ability to manage larger groups of friends/enemies/enemies of friends/etc. Within this you would be able to create a community with a group of buildings like a small town almost. This falls back into having a group leader to manage things instead of everyone out for themselves. Maybe even as the game progresses you “restart” normal humanity, or at least within your small area that you have.
These are just a couple ideas I have that I feel that would make this game playable for years to come instead of just playing it until something else comes along… at least in my eyes.