In the long run I can imagine a more fletched out AI diplomacy setup. Races going to war to achieve certain wargoals, not necessarily extermination of the other race but maybe just making them a client race which can be liberated by the player or more benevolent races, conquering outposts perhaps starbases, financial and material resource exchange (with a more meaningful resource model like certain amounts of resources needed to build an armada or the lack of them slowing down production rate) etc. Basically, introducing more assets with which the AI's can play around and settle conflicts even by their own perhaps even on the negotiations table before war is declared. Sure, this goes in the direction of Europa Universalis 4 and similar games but I think there is a huge potential and it could keep the game alive for years to come.
However, right now this is more for future expansions and we should concentrate on the system we have currently. This means more war and less diplomacy unless the player intervenes. There is not much the races can do except to prepare for war and go to war eventually if left unchecked by the player.