I really would like to weight in here as during the last 3 years I have been talking about this to Steve in multiple posts.
However, since I first talked about Aurora's diplomacy and while waiting for either 7.2 and now C# to come out I have increased my amount of RP with the game. The main reasons were the slowdowns, the lack of diplomacy, etc, etc. I have then after multiple games (one lasted a year in RL with probably 10mb or more Word file with multiple spreadsheets aside) reintroduced NPRs as Steve said and I've found to be true that when you have multiple factions in Sol it always end up same way: one race go to one direction, another goes in another direction and so on. Practically unless you RP it there is no need for war at all. I am getting to the point no worries. The main reason I reintroduced NPR is then the following: you need some containment to your expansion otherwise you'll never face problems like the need for a better planet or a colony, lack of a particular mineral or simply your minerals are running out and you need new ones. And therein, as the Bard would tell us, lies the rub.
With the current way Aurora is structured you WILL ALWAYS end up wiping out the competition as you will need to expand for more resources, better planets, etc.
So after many reflections even over my previous requests, I believe that the only way to make diplomacy actually meaningful will be for the Human Player and the AI to be able trading minerals and resources.
I am saying that because despite all the previous posts are true and would be nice to have good neighbors or to find a sort of equilibrium and "grow tall" rather than wide I cannot see how this can actually happen. Many paradox games and many other grand strategy games or even 4x games do not have the finite resources factor. I think few do but I cannot really think of a worth noting. Yes, they have a pool of resources and manpower (Aurora does have manpower too by the way) but the source of them is infinite.
So basically I stopped being obsessed with better diplomacy (which will still be great especially the minor wars and territoriality being added in C#) but I really believe that if the above cannot be sorted/fixed at the end war is inevitable so at that stage why wait for the enemy to strenghten his position?