There's another thread about the calendar use that got me thinking... sometimes things that don't affect gameplay at all can have a big impact on the way a game feels. It's probably late in the game to be suggesting gameplay design choices (also difficult to do without having played), but usually aesthetic choices are more feasable to add later in development.

What are some non-gameplay features in other games that you think really made things feel more immersive? Or what are some ideas you have?

I'll drop a few ideas in the comments to start.

World Map - Center of the world

I don't remember which Civilization game it was, but in one of them your world map would be centered on your capital until developing a specific tech... I think compass or map making, then it'd be centered the same for every player.

There could be a lot of fun with this. How do we define the center of the world? Right now in real life, we all follow a time zone centered in England. The Americas all center their world map on Europe.

Maybe the first civs to reach specific milestones spread their influence on the other players. Center the world map on whoever develops compass first, or maybe whoever collects the most fame during a specific era.

Calendar

Just linking to this thread that's already talking about some calendar stuff. That was what got me thinking about it in the first place. https://www.games2gether.com/amplitude-studios/humankind/forums/169-game-design/threads/35855-holocene-human-era-calendar?page=1

Here's one we've been told will happen: the Avatar's outfit. Basically, based on the cultures you choose and the kind of actions you take over time you're outfit will change to reflect this.

So, here’s something along these lines I’ve been mulling around—from an in-game story perspective, how did the cultural transition from the old current culture to new culture take place? E.g. How does an expansionist Assyria shift to a merchant Aksumite? By selecting a new culture in Humankind, you are evolving into that new culture’s identity, visuals, and gameplay style. However, you still retain some characteristics from your previous culture including some visuals of older buildings and cultural bonuses. I think many of us are history fans, and it’s been a bit challenging for me to reconcile how, the Babylonians could shift into the Goths, for example. Obviously, this is total alt-history territory and the dates, geography, etc. for these cultures don’t line up, so they never could have interacted in many cases. But after thinking on this more, I found this was actually a fun thing to noodle. 

So keeping in mind the cultural traits for each culture, how would a culture such as, e.g., the expansionist Assyrians shift to become the merchant Carthaginians or builder Mayans? I am assuming that the new culture (the Classical Age culture) supersedes the old culture (Bronze Age culture) but is not a total replacement. While most of the old culture evolves to the new culture, some legacy traits remain, so this is more of a hybrid culture not the true culture from real history. The player becomes the “Assyrio-Romans” or the “Egypto-Romans”, not the true Roman culture from history. The possibilities for how these Bronze Age cultures evolved into their Classical Age culture makes for some potentially fun stories to tell… So what if, based on the decisions you made in-game plus obviously who you select in the next Age, the game could generate a story about how your culture evolved? That could be a flavorful and immersive addition to the game. And even if this doesn’t ever happen, I can make up my own head-canon stories anyway :)

Here are a couple examples:

Assyrian Goths

Over the years, Assyria came to rely more and more on foreign mercenary armies to fuel their never-ending conquests. One particular group of foreign soldiers, from the dark forests of the north, known as the Goths, proved their valor and bravery many times over. Over time, these Gothic warriors came to be trusted in important and key posts within the Assyrian military, even being given generalship over mighty Assyrian armies from time to time. Later on, the Goths were given an unprecedented honor by one Assyrian king, forming an elite bodyguard unit in charge of protecting the Assyrian royal household. At one point, one particularly noble family of these Goths were even brought into the royal house through marriage. Eventually, after a succession of ineffectual and weak kings, the real power behind the throne, the elite Gothic warlord who had held high command over the military for many years, overthrew the Assyrian king. Now, this newly emboldened and strong Gothic-Assyrian dynasty promises to reinvigorate a new, fresh round of conquests for the Assyrian Empire.

Assyrian Mayans

Word of the Assyria's power stretched far and wide over the ancient world, carried by the gossip of traders and merchants, eventually reaching the distant lands of the Maya across the vast Atlantic Ocean. A Mayan prince, being brave and adventurous, decided that he had to see this mighty Assyria for himself. Traveling with an entourage of warriors, craftsmen, and priests, the prince made his way over the long distances, across the great ocean, eventually arriving in the Assyrian court. The Assyrian kings were amazed at these exotic foreigners from distant lands and diplomatic relations were quickly established upon the prince’s return to Mayan lands. The Mayan prince eventually settled in Assyria as an honored guest and made fast friends with the nobility—including the chief architects and builders of the Assyrian realm. Sharing the Mayan secrets of architecture, the Assyrian nobles and their architects became enamored with Mayan skill and craftsmanship at building vast and impressive stone temples and palaces. Over time, the Mayan influence at court grew from architecture to influencing other Assyrian cultural practices. Now, the Assyrian kings, who have admired Mayan ways for generations, seek to build upon and improve their own cities and build temples and wonders reaching to the heavens, worthy of the both the Maya and the Assyrians of old.

I think your stories already went into the direction the game wants you to. Instead of giving you one backround story for the cultural change, it might hint your imagination into your own story for your entire cultural evolution. While your idea is nice it might also restrict the fantasy of a player like you, who is obviously capable of writing his own story. ;)

Ooh, what if you could submit your stories at the end of the game and you have the option of having another random player's story showing up during the transition? They'd have to be screened, obviously, but that would give both creative players a chance and those who want to just read a cool story.