One point of era score in relation to Secret Societies. For example, recruiting unique units, building unique buildings and getting all four promotions. Maybe something similar for unique City-State units and tile improvements.
Era Score for splendid adjacency bonuses applied to unique districts since you get the Era Score in relation to unique units, the use of a strategic resource and first ocean unit being the notable ones.
The ability to renew friendships/alliances and renegotiate trade deals/open borders when they end without having to redo the whole process from square one. It is endlessly aggravating moving units through other civ’s territory and having an alliance or open borders end and then have to send them back through the territory you were already moving through in addition to them thinking I am going to declare war on them and then break a promise because I still have to move troops through their territory. Or the only way I have to find out that a trade deal for luxury resources expired is that all of my cities are now unhappy. Having to constantly recheck to see if I still have open borders late game going for a culture victory is equally exacerbating. The ability to renegotiate trade deals and alliances right when they ended would make the game so much more pleasant.
The ability for a permanent alliance after you have gotten a level three alliance.
The ability to ask an AI to move troops away from your borders and to get a casus belli for a War of Retribution if they don’t.
The ability to immediately break an alliance if an AI breaks a promise or declares war on a city-state you are suzerain of and no penalty for any related wars.
Alliance blocks between three or more civs. For example, if I am allied with two other civs and they are both allied with each other than we could form an alliance block. Alliance blocks would be able to share resources and maybe get some boosts. Say I am going for a science victory and I have low faith and culture output and my two allies are each strong in one of those I get a boost or some kind of per turn yield in culture and faith from them and they get a boost in science from me.
Research Agreements from the base game are far better than what is available via a research alliance in the expansions and should be brought back in some way, even if it is limited to being in a research alliance. Especially since they are still useful when going for a science victory, unlike the alliance.
A nonaggression pact, unlocked with Civil Service, that prevents you and another civ from declaring war on each other, even if you would normally do so because of an alliance.
The ability to make “horizontal” national parks in addition to “vertical” national parks. Also, the ability to choose the tiles that make up a national park if there are more than four valid tiles in a close area.
The ability to become permanent suzerain of city-state if you have been suzerain for something like to two whole eras. Also, a casus belli against a civ or city-state in such a relation to become the new suzerain of a city-state in that type of relationship. More interactions with city-states generally would be welcome as well.
The unique melee units from Military Tactics need to be better integrated into the melee unit class, either replacing the Swordsman or changed to being a Swordsman upgrade that then upgrades to a Musketman. They could also be moved to another tech as unlocking a unique melee unit from a tech that is boosted by the Spearman is just kind of weird.
To choose which tech boost or great work to steal on their respective missions when using a spy.
Spec Ops should be invisible unless next to an enemy unit, Encampment or City Center to make them useful. I know it is the final promotion but getting to that final promotion is incredible hard to do. Also, maybe additional sight range for recon units upgraded to Corps and Armies.
The Inspiration for Humanism needs to change because the only way to reliably trigger it is to be going for a Theater Square heavy culture victory. All of the other inspirations and eurekas are, aside from the religion focused ones, achievable when going for any victory type. Maybe changed to recruiting a Great Artist OR Great Engineer given the fact it unlocks the Invention policy card. I would like to see some "Or" options for eurekas and inspirations generally to add some more variety to the game so you are not repeating the same patterns game after game.
Infantry should require niter, not oil, given they are almost immediately and severely outclassed by tanks as well as the fact that oil is also used by artillery and they are all unlocked near each other. They also don't require it in real life and it has always seemed strange to me they do in the game. Mechanized Infantry should still require oil though.
The Inspiration for Suffrage needs to change as building Sewers has nothing to do with the play style preferred by the government unlocked, unlike the inspirations for Class Struggle and Totalitarianism. It should be something like have three alliances or something similar. Alternately, move Sewers to earlier in the tech tree and have that be Inspiration for Sanitation (which gets some a new building or something, maybe that encourages extra population growth) and have building Neighborhoods be Inspiration for Suffrage, which makes far more sense from a game play perspective (decent extra housing for the extra food) and a theoretical one (more citizens mean more calls for inclusion and say in governance). Along with this if Sewers are not going to come earlier in the tech tree then they need a buff as they are really weak for a late game building.
Better differentiation between alert sounds. The alert sound for your spy has completed a mission and an enemy spy has successfully completed a mission against you are the same as well as the sounds for someone has declared war on you and someone has declared against someone else who is not you. It is very annoying/nerve racking, especially if you are not constantly looking at the screen when playing the game.
Late game spy satellites, a Spaceport project, that removes frog of war from parts, or all, of the map. Unlocked sometime after Rocketry.
A late game, maybe with unlocked with Chemistry, Builder or Military Engineer ability to turn hills into flatland or vice versa. Alternatively, unlocking Chemistry removes hill/flatland requirements from districts and wonders that have them.
A late game “autopilot” for cities that converts production into Science, Gold, Culture, and Faith instead of having to queue up district projects.
The Eurekas for Square Rigging and Naval Tradition should be changed. Naval Tradition should be to recruit a Great Admiral which makes sense for the Policy Cards unlocked since you really only need one coastal city or harbor to build a Quadrireme. Square Rigging’s Eureka does not fit with similar Eurekas which have an entire era between unlocking the unit needed and the tech with the corresponding Eureka. Changing the Square Rigging Eureka to killing a unit with a Quadrireme fits the established pattern perfectly. Also, the tech is called Square Rigging and I'm not sure what that has to do with Musketmen.
Purely an aesthetic change but the Eurekas and Inspirations descriptions should be changed to fit with unique units, districts and buildings. So, Electricity’s Eureka is changed from saying Privateer to Barbary Corsair or Sea Dog for the Ottomans and England respectively.
Map generation should bias towards making it impossible to circumnavigate the world without unlocking Cartography first. Way to often on Standard map sizes I can circumnavigate the world by just unlocking Sailing and Shipbuilding and it feels weird to do so. Also, continents maps should not generate a Pangaea type land mass, which has happened more than once to me.
Zen Meditation should be changed to one amenity for every two districts, including the city center if it already doesn't.
It is way too easy to generate culture outside of the Theater Square while science is almost impossible to get outside of the Campus. This is compounded if you have a religion because good Holy Site spots compete with good Campus spots. The available methods to generate extra Science are way to random (the Zoo and Aquarium) and Military Research policy card has too many limitations and is limited in scale. There should be a midgame science equivalent to the Monument so you can get more science. Also, maybe Encampments and Industrial zones can provide major adjacency bonuses to Campuses as well.
Dido’s Move Capital project needs to be cheaper but as a tradeoff maybe limited to once an era. Also, maybe entering a Golden Age allows any civ to move their capital at the the start of the era as long as they are not a war and haven't had their original capital conquered already.
A map search function for consoles versions of the game. Especially needed given the newest game mode that has been released.
Decommission Power Plant project should be unlocked with Environmentalism instead of the Climate Accords competition.
Along with the regular difficulty settings there should be a version where the AI bonuses are halved or more but scale up, eventually ending up surpassing the current bonuses, with each new age in the game that way it is possible to get early wonders while making the late game more difficult.
Game and Map seeds should not be saved when you save a game configuration.
Some more military units. A melee unit for the Medieval and Industrial Eras that are part of the upgrade path for the unique units from those eras. A new Medieval unit should also be in a new tech instead of Military Tactics, which is boosted by unlocking Feudalism since it has the corresponding production discount policy card and Stirrups would be boosted by training to two Horsemen. Heavy Cavalry for the Classical Era and get rid of the Heavy Chariot. Siege units for the Medieval Era. Maybe a Classical Era naval raider unit. A ranged cavalry class because having the Saka Horse Archer and Keshig upgrade into Field Cannons makes less useful compared to other units.
The boost for Castles needs to change because at this point it is functionally adopt Monarchy, not a tier 2 government.
The Inca’s Terrace Farms should count towards the Feudalism inspiration or replace regular farms as the inspiration.
Chandragupta should get a grievance discount similar to the one Cyrus gets.
Autocracy and Monarchy legacy bonuses are kind of weak and could use some improvement or just changed outright.
Shipyards should give +1 production to all water tiles.
Liberation Wars should apply to city-states that were captured if you were suzerain or had a certain number of envoys at when it was captured.
An alert function for Inquisitors.
Joint peace options for ending a war for when you go to war because someone declared war on one of your allies.
Some type of improvement, even if it in an unique improvement, that can be put on marshes.
More alternative Leaders for existing civs. It seems like it is the most underused feature of the entire game and Kublai was a wonderful edition to the game and works well with both of his civs, unlike Eleanore. Personally, I would like to see a new leader for Japan that mirrors Hojo’s district discount ability for the districts he doesn’t cover. I would like see more Leaders with unique governors, tile improvements, buildings and a leader with an unique district.
Policy cards like Inspiration and Strategos should be updated to mirror the recent changes to the late game policy game cards that replace them along the lines of some like +2 Great Scientist points plus +1 per Library for Inspiration.
Do something about the late game AI settler spam that involves them settling a one tile island, settling where they have no chance of maintaining loyalty or just endlessly wander the map with the settler. It seems the AI thinks “need new city” but doesn’t factor in whether or not there is actually any good places to settle.
A way to see which cities DO NOT have trades routes going from them that doesn't involve getting out pen and paper and doing a process of elimination, which becomes especially frustrating in the late. Same for which other civs you don’t have a trade route to.
Some kind of buff to the Diplomatic Quarter, like giving governor titles for finishing buildings.
Change the Inspiration for Theocracy to something like having three Holy Sites so it can be gotten by civs that didn't get a religion. This would help with unlocking the government as well as getting the boost for city-state quests. The Inspiration for Monarchy would have to change as well but I don't know what to but something preferably that would play to a domination victory. Maybe change the civic tree around as well so that you don't need to unlock Monarchy to to Theocracy.