I want to adjust the tech/civic tree, maybe add some more techs. It seems pretty sparse as-is.
I'll have to see how it plays for balance, but I'm leaning towards stronger interaction between the two.
I'd also like to change Eurekas and Inspirations. Instead of giving half of the research for free, I'd increase the rate at which the tech is researched by 100%. If you haven't started the tech yet, this functions the same, but it won't finish the tech if you're half way through, only cut the remaining time in half.
I feel like the tech tree is way too easy to skip through right now.
Finally, I'd like to add semi-requirements. Similar to Eurekas, maybe a tech or civic isn't required to research another but having that tech helps you but not as much as a full Eureka would. For example Celestial Navigation is a dead end tech right now, but maybe having stronger navigation skills impresses the need for better and more sea-worthy ships? Not exactly a full Eureka, but helps you along with research. That's a Eureka type example, as Civ 6 explains it, Eurekas are an impetus to research not actual knowledge (another reason why I don't like giving science for free with Eurekas).
The other type of semi-requirement would be something that actually helps you figure something out. For example, Cartography doesn't require writing right now (lol), so the knowledge of writing would improve your ability to make maps.
Honestly though, that's a horrible example because Cartography should absolutely require writing. It just shows how poor the current tech and civic trees are.
Current ideas for starting to adjust the tech and civic trees are: wheel comes from animal husbandry, not mining. Bronze working comes from pottery and mining, not just pottery. Irrigation comes from mining, not pottery.
For civics, replace code of laws with chieftanship. (Code of laws is formalized much later historically), change international trade to just "trade", make mysticism available earlier with no requirements, add rituals which requires mysticism, add proto-government which requires trade and the discovery of the writing tech.
That's about all I have so far. I'm aiming to flesh out both trees, make the interaction between the two more important and spread the eras out longer. I think culture and technology should interact more heavily than they currently do. Neither has ever existed by itself.