I mentioned this in another idea but I think it would be interesting if the kind of enemies, events, and other gameplay features could be activated/deactivated via Mod List or in another tab for official modules in the World Creation menu. Some examples:
Undead:
-Zombie and skeleton version of humans and animals.
-Urban areas populated mostly by undead humans. They do not respawn.
-Wilderness populated mostly by undead animals. They respawn.
-Undead attack all living things and ignore the rest.
Nuclear Winter:
-Colder overall temperatures with winter being almost deadly outside.
-Harsh Storms and chance for radioactive rain.
-Radioactive areas in the world.
Steampunk:
-Weapons and electronics replaced by steam-powered and clockwork tech.
-Neo-Victorianism clothing, buildings and furniture instead of the normal ones.
In addition, some modules could offer extra features if activated along with compatible modules. For instance:
Blobs/Zombies:
-Blobs and Zombies are allies.
-Blobs can reanimate dead corpses.
-New type of zombies available.
Steampunk/Robots:
-Robots are replaced by steam-powered and clockwork constructs.
Zombies/Bandits:
-Urban areas populated either by undead or bandits. They do not respawn.
Of course, some of them would be unable to be chosen, like Nuclear Winter and Nuclear Summer, for instance.