I have to say i too am curious about the Diplomacy, moreso as im a little perturbed by having heard people say the other factions will generally always declare war on you early on.
I was hoping the Ai would allow for now expansionist or martial type opponents as well, so that we could meet a neighbour who doesnt want to fight they just want to trade or have peace at any costs...so that you get a mix of AI personalities not just one type, one approach to the player etc..
Going back to GalCiv my preferred play style always used to be the influence method, focusing on diplomacy early on so that you could effectively keep the neighbours passive while you could then play the long game and build up strength and influence in relative safety while the other opponents fought amongst themselves..and then when the time was right because i'd had that long period to build up in safety, sweep across them with relative impunity.
Not everyone likes to go full combat approach and Im hoping diplomacy and the enemy AI's in this game will also provide for that style of approach as GalCiv2 did.