Right now, at the start of a new game the overmap is generated, but the actual maptiles aren’t created outside the player’s reality bubble. Those only get created when you move close to them. Using the .json method, each maptile has an id, but there can be multiple variants with the same id. If there are more than one, the game picks one based on their relative “weights”. So if there are 3 variant tiles with a weight of 100, there is an equal chance that any one of them will spawn.
But instead of weight being a static number, it could be based on a timer. That would allow variants to become more or less common as time passes. Like, if you had three variant houses, normal/looted/wrecked, with different timers, you would only find normal houses early on, then looted and wrecked would start to show up. After a few years, normal houses would become a rarity, and towns would be mostly burned out wastelands. The world would seem to be evolving as time passes.
For one, this would allow NPC encounters that make some sense. The first season you could encounter normal citizens boarded up in their houses, a year later you would find grizzled survivors, and a few years on you might find heavily fortified gas stations defended by colonists. It would also be a way to add more end game content that shows up in the end game. You could make maptiles with high difficulty/high reward without worrying about destroying some poor day 1 survivor (or giving him a suit of power armor).
I thought the timer could have 4 values, a start weight and end weight, and two dates. So a looted house with 10/200, 14/122 would have a start weight of 10 until day 14, then it would steadily climb until day 112 when it would reach it’s final weight of 200. That’s just an example though. There are probably better ways to do it.
Of course, this would only apply to newly generated maptiles, so your starting area wouldn’t evolve. You’d have to travel to find later stuff. And there would be weirdness with multi-tile overmap specials. If you drove past a mansion on the first day, causing only half of the maptiles to load, and then came back a year later, half the mansion would be pristine and the other half would be looted. That might not be a serious problem.
There are cool tricks I could do with overmap specials too. Like I could make an apartment tower called bandit_tower. If you encounter it early on, it would be just be a normal apartment like any other. But on a certain date, the weights would switch from the normal tiles to the evolved version. If your first visit is after day 56, or whatever, then it will be occupied by Hells Raiders. And after day 112, it would switch again to a fortified base with even more enemies and traps.
The drawback is that this would require lots of .json variants. So even if a timer is implemented, it will be a long time before people go through and make evolved versions of existing structures. It would also mess up a lot of people’s current strategies. Early reading and crafting would be penalized because the timer would be slowly reducing the frequency of safe loot in the world.