I'm very wary about this.
First, the diplomacy in Sins is really bad and needs changing. That's fine.
But 'diplomacy tech'? Diplomacy ships? Cluttering up the game more isn't necessary to fix the mission-based diplomacy (hell, allowing the player to accept missions or propose them would pretty much instantly fix the diplomacy as it stands). Yet Another Tech Tree and single-use ship doesn't sound like a good direction to go.
Entrenchment was great though, so ... we'll see.