Sins of a Solar Empire will release in winter 2010. The Diplomacy add-on will increase the number of ambassadorial options to players in their conquest of the galaxy. You know, sometimes it helps to talk through the issues. Ironclad and Stardock plan to have a beta for the expansion this fall in order to work out any Vasarian bugs.
Entrenchment and Diplomacy have both suffered delays while jumping into the digital distribution galaxy. A third micro-expansion for Sins was previously announced, so the full 4X RTS space opera experience should be completed sometime next year -- unless there are more delays, of course.