I would very much like to see the Harbor provide some tile bonuses to sea tiles. Food and gold bonuses would make sense. Perhaps we can even diversify? Research Lab could provide a Science bonus to coastal and sea tiles. Hotels could add culture or gold.
So much of human life revolves around the sea. I know a solid effort has been made to make inland cities competitive, but I'm not certain that's in the best interest of the game. The world's superpowers have almost entirely been coastal for a reason, with the exceptions notable for being a rare exception. Until modern times, landlocked nations simple could not compete.
As far as the diplomacy modifiers go, the biggest issue I have is all the positive modifiers require you to already have good relations. Declaration of Friendship and Open Borders are the largest modifiers that don't involve war which I'm aware of. If I've slighted someone, sometimes without even intending too, there's no climbing out of that hole. Right now I have someone that's Hostile because we're competing for the same city-states, competing for the same world wonders, my behavior worries them, and my recent diplomatic actions disappoint them. I met them ten turns ago in a 200 turn Epic game. The little bonus I have from an embassy and lack of contested borders means nothing in the face of those modifiers. They won't sell me open borders for 100gpt and 3 luxuries, so there's no real chance of converting them to my religion (which is seen as a hostile action if they have founded a religion). Giving people gifts through the diplomacy UI seems to have no effect on their opinion of me. Giving in to their demands has no positive effect, failing to do so has a negative effect.
Diplomacy feels like a tightrope walk. There is a very specific playstyle that will stop someone from hating you, and one slip is all it takes to be heading down the path of irrevocable eternal enmity. I don't know the right solution for this.
As for ideology, I currently have DoF, mutual DoF, open borders, adopted my religion, no contested borders, embassy, and trade partners modifiers with Theodora. According to transparent diplomacy, that's +83. Last time I checked, the Ideology modifier was larger than that. Even if it isn't, if we pick differing ideologies, she will befriend those of the same ideology. Some of those will denounce me, and then she will denounce me and end all of our positive arrangements. I have no method of influencing her towards an ideology that allows us to stay allies.
Generally, I feel pretty powerless to effect international relations through peaceful methods. Non-peaceful methods are being punished more harshly now that there is a global penalty for killing civilians. My options seem to be polarizing towards 'stay in my corner and don't bother anyone' or 'take up the sword and burn the world to the ground' with no option for making a strong ally that I can peacefully coexist with as I grow stronger.
Side note, it's nearly Turn 200. I have fully converted Theodora to Islam. She has not founded her own religion, and is in late Classical age. She grabbed Earth Mother fairly early and has a Jade heavy start. First time I've seen this behavior from her.
