Decolonization and new civilizations. I like humankind very much and it is perhaps the only video game I play, after having played all the various civilizations... This title is the most realistic. But there is still room for improvement. especially on the concept of civilization levels. rise and fall of empires. I would like to interact with more than 9 other civilizations, and in fact I always try not to eliminate them from the game. I would like it more, if as time goes by, new ones are created. a bit like the USA was born from a piece of the British empire, or Brazil detaching itself from the Portuguese one, which in the meantime has not ceased to exist. One could evaluate the concept of cultural unity of civilization, and where this fails, have independence movements, as if a rebel leader were born who starts as a vassal. Another aspect that I would like to be reproducible is that of the invasion of the Roman Empire by barbarians who then created their own civilization. why don't minor peoples, instead of going into decline, transform themselves into other civilizations, with their own leaders? In this way you can have a replacement of opponents in the continuation of the game. Finally, you could have a prison room, where you can collect defeated leaders, who can be given to other civilizations through diplomatic channels, freed as vassals or kept as a trophy to earn points at each turn.

I would like that. And it's not like it's impossible or hasn't been before:

For instance, the well-regarded Civ IV mod Rhye's and Fall of Civilizations modelled human civilizations roughly when they appeared on the world stage, including dynamics with factions that already control that land and can lead to their demise. Heavily scripted but an interesting experience.

Another Civ IV mod, barbarian civs, allowed for barbarians (independent peoples in HK terms) to settle down and eventually become full civilizations. They wouldn't typically be major powers because they'd effectively start with a big lag. But it would lead to rather interesting dynamic around client and buffer states, proxy wars etc.

Aside from Civilization, one somewhat underappreciated (but also below its potential) game - Dawn of Andromeda - had minor species that would eventually become major ones if left alone and/or sponsored enough. And even you as the player might start after some other factions such that they are already more established at the start of the game.

And if I understand right, Old World's higher difficulty levels effectively also have you start against already partly established factions. Not quite the same as mid-game changes but still a bit of added variability.

All that being said, with the limited pool of cultures per age and this being a very deep gameplay change, I don't particularly see it happening for HK. Maybe for a huge future DLC or a HK2 if they ever do one.