[gameplay] Dump the Diplomacy Tree.
Diplomacy is based on interests, and while it can be said there is a certain amount of science involved, that tends to go into some pretty dry details for a fantasy game. Playing as Gilden with Relias as my neighbor, he repeatadely begged me for help against the powerful Kraxis. I was ready to form an alliance and go to his aid, but alas, such assistance had not been invented yet.... I have no options to form an aliance or to gain any kind of military access, and his territory blocks me from accessing Kraxis territory.
That's pretty silly...
In Civ4, you also needed tech to form alliances and such, but that game doesn't really have the 'good vs. evil' thing going on, and also there isn't a whole tree dedicated to diplomacy. By the time you might want to enter an alliance, you usually have the tech which also gives other benefits and research paths that you needed for other things.
Why do I need technology just to help someone who asks for it? It's kinda goofy to imagine a society that is progressed in every civilized way, and utterly stone aged when it comes to diplomacy. You have to be somewhat diplomatic just to live in a city. Having a diplomacy tech tree is not really compatible with the nature of diplomacy.