One thing that's always broken the story experience for me in games like Humankind is how far scouts can travel and how much of the map can be explored and revealed, particularly in the early game.  What if the fog of war remained more permenant, not just going to a tinted map (where you still know the terrain features but can't see what activity is taking place), but reverting back to a dark/covered map until your units have traversed over an area a certain amount of time, or until land is within a certain distance of your borders (political or cultural)?  That would be a more realistic way of developing maps, trails, and well known routes through land that is not settled or influenced by you.  It would also make it difficult for units to return or navigate the most efficient routes back to known territory, making travel further and further out both more risky and more time consuming.

I also think playing around with some form of logisitcs or supply would be a good way to limit over-exploration.  Units morale should decrease, healing should be more difficult (perhaps even small amounts of attrition, which could be boeyed by finding resources or meeting other people), or some other mechanism that puts your unit at risk of being lost if they venture too far.

Contact, trade, and other exchange with foreign people would thus be more valuable, as you could trade for map information, like routes through moutain passes, the quickest route to their nearest city, or other such ways of expanding your knowledge of the world terrain without actually having set foot there.  Perhaps, for example, instead of your unit crossing a tile say 5 times before it remains revealed in a fog of war state and not totally darkness, maybe if another civilization has knowledge of that terrain that they've shared with you, your units only need to cross it twice, say.

There's a lot of creative opportunities with exploration, the units doing the exploring, interactions with other cultures, and other mechanisms that could really make the early game and periods of expansion much more interesting and realistic to the arc of human settlement. 

It sounds like the early game could turn into a memory game/screenshot fest with unsporting players, but otherwise I really like this idea. Maybe a togglable option for people who play singleplayer or multiplayer with friends, but don't otherwise want it for online multiplayer? But then it sounds like a bit of a pain to implement if it's just a toggable option... I think maybe we'll see a game that has this features one day, but I fear Humankind will not be that game. But maybe, as an option, if we're very lucky.

Logistics/supply would allow exploration to be limited while not needing for things to be "covered back up" and needing a memory pad nearby.

Something like if distance to nearest city/outpost >X, takes damage over time. (X is higher for exploring units and increases with eras)