That's really tough, there are a bunch of huge features that might not happen outside of magical intervention.
Probably the hordes system and associated subsystems like fire spread and NPCs roaming around scavenging things.
The thing about a proper hordes system is it essentially makes the active area of the game bigger, so now you have to worry about things in earshot and things that you previously interacted with instead of just things you're looking at in the moment.
while i definitely want hordes most of the things you'll hypothetically get to someday, i was really excited for a little while at the idea of the sun tracking that almost happened. that sounded so cool (and with our increasingly viable 3d fov stuff, could LOOK cool in our modern rendering)