It'd be nice if when offering missions you could give an AI a mission to send an envoy to another AI. I was playing a Random Huge Multi game today, and after obtaining peace treaties with 3 AIs, the AIs proceeded to shoot each other to death, causing me to pick a side or risk losing favor with all of them. It'd be a great feature to be able to encourage peace between AIs to create fully functional alliances. Even though it's possible to have alliances with more than one other person, in a 10 player game having larger alliances would add to the replay value (and flavor, especially with the Vasari Rebels) of the single player experience.

Considering that changing the valid target of a mission isn't exactly a huge time investment (at least I'm assuming it's not), it seems perfectly possible to implement this into the game before it comes out. It doesn't require any new particle effects, sounds, or art assets, just a few minutes of time to change a couple lines of code.