Background and History: Newcomer Atsurecachure created a new thread today, "Why the Culture Change Mechanic Was a Bad Idea", which proposed that the culture change mechanic that's foundational to Humankind was a bad place to start.  It's not very constructive, and I disagree with many of their points, but there is a good kernel near the heart of it:  because Humankind has empires transitioning from one culture to another over the course of the game, and because we add each culture's legacy traits together into a mosaic of powers, any combination of cultures must be viable and any combination of cultures shouldn't be overwhelmingly powerful.  As we advance through the eras, we keep our Emblematic Quarters, we keep our Legacy Traits, and while we can hold onto our Emblematic Units, they do naturally become obsolete.  The only thing we truly lose as we move from one era to the next is our ability to build more of our current EQ, and we lose our culture's Affinity if we take another. All of this combined means that the cultures of Humankind aren't as diverse and gameplay-affecting as the factions in Endless Legend or Endless Space:  We can't have a culture that leans as far into stealth as EL's Forgotten or ES2's Umbral Choir, or the one-city-specialists of the Cultists, Mykara, or Choir, because each culture needs to play nice with the cultures before and after it.

But what if each culture were allowed to be more "extreme" at the moment where they are ascendant, without impacting the later parts of the game?  The Aztecs were conquerors until they were themselves conquered by the Spanish, but today, none of their successor states in Latin America anywhere else in the Hispanosphere continue that tradition of conquest, though they are undoubtedly touched by those earlier cultures.

Proposal: Add to each culture a fifth property alongside their Affinity, EQ, EU, and LT — an "Ascendancy Trait" that is only active while an empire is that culture, like a supercharged Legacy Trait, but one that disappears when an empire moves on to another culture.

Some cultures already have legacy traits or other properties that could make sense as Ascendancy Traits: Huns and Mongols (and Singapore) can't found new cities, strangely, and therefore they have a slightly different gameplay.  Embrace that, and embrace giving cultures game-defining temporary handicaps and game-defining temporary boons.  The Mongols could have other powers that support a broad empire of conquest: No penalty for going over the city cap, to start with.  The Norsemen boost to naval units could be a huge boost while you're the norsemen, but shrink down in the Legacy Trait.  The Venecians and the Ghanaians could be undisputable trade powerhouses with even greater powers over trade and foreign politics for as long as they remain the Venecians or the Ghanaians, but once you're done with them, you still have a nice legacy of trade.  How terrible would the Aztec Empire have remained into the Early Modern Era if it weren't conquered?  Some cultures like the Goths might not gain science the normal way (like the Forgotten or Nekalim), or interact with other FIMS differently.  If you're lacking for industry, then maybe you can pick a culture whose faith is added to each city's industry?

Any of these powers seem too extreme to have as a Legacy Trait, but could be gameplay defining for the era you're playing as them, allowing for huge swings in gameplay and even "dark ages" as you pivot from one era to another and lose a key benefit you've been playing with.  Each culture feels a bit less vanilla, and the whole game becomes a richer tapestry with more meaningful differences in each playthrough.