Not so long ago, I mastered the Development Tools editor and started creating my own rebalance of the game. These are the ideas that came to my mind:
Scythia - An additional Light Cavalry unit is generated from the previous era. That is, by creating a horseman you will get barbarian cavalry, courcer will create a horseman, etc. Saka will be created as usual. With their bonuses, even backward units without upgrades can serve well in battle. Along with this nerf comes the Kurgan buff - for each era after construction or last repair, it gives +1 culture, while not being destroyed by cataclysms. Just like the Zoroastrian temple in the game. Also, tumulus cannot be created in the desert, tundra, and snow (the very idea of this is absurd, now such a limited location is compensated for by a really powerful potential in the late game). In the future, it can give cultural tourism. This ability is reflected in the properties of civilization, not improvement, that is, the invader of the cities of Scythia will not receive culture bonuses, but will be able to enrich himself well by plundering Scythian gold, since now the loot for looting is in gold instead of faith, and its amount is twice as large as usual.
France - chateau opens in castles, gives +1 culture to each neighboring cell with the prestige of 3 with the opening of humanism (invited painters begin to live in noble houses). Also +1 gold for rare resources. But now, in addition to the location by the river, you can not build two chateaux next to each other. Now it turns out that the bonus from wonder rather allows you not to lose the main bonus of the chateau, and not its main role.
Eleanor - +3 to all cavalry units, for a victory they bring 5 points of the great writer. The bonus reflects the reckless crusades and the troubadours who chant them.
Genghis Khan - the +3 bonus is given to Eleanor, instead the Cavalry gets +50% combat experience. In addition, pastures and camps make a cultural bomb. In Australia, the bomb will be moved to the Outback Station.
Norway - The ship production bonus is replaced with a +1 production from Stave Church, which is now stripped of it, but is in drama and poetry and costs half the price of the temple. Berserkers can be bought for faith and give 40% of their value in faith when they die.
Korea-governors give +3% faith instead of science. You can hire warrior monks in the shrine, without the appropriate religion (the warrior monk belief will be improved, with it, cities with a temple will give +25% experience to all ground units before the industrial era, and recon units of any era). Seowon gives 3 sciences initially. With the opening of the writing, an additional governor's title is given.
Even before the announcement of the patch, I managed to improve the Khmer so that farms gave +2 food for dams as well as for aqueducts, and, most importantly, when building a dam or aqueduct, a free builder was given. The holy places received bonuses from the proximity to fresh water, not just the river. And Spain just gave from me a +1 bonus to everything from the palace, as in the autocracy (a reference to the unique palace-monastery-library El Escorial in the name of Philip's ability. The final version of Firaxis really shocked me, so much of the cornucopia for Spain I did not expect) But these nations have suffered so long because of their unreliability that they really deserve to be an OP in their old age!