The next Sins of a Solar Empire expansion packed entitled Diplomacy is scheduled to hit a public beta this Fall, that according to a Stardock employee blog post. Diplomacy will add new diplomacy features and new diplomatic tech-tree options to research, including the ability to form treaties with other alien races and trade treaties with other races.
So instead of firing guns and blowing up star bases, your co-op sessions can be a little more peaceful. But where's the fun in that? Expect Diplomacy to be available next Winter after an extensive beta.