For settings with locked teams and no pirates, how will diplomacy actually effect these games?
The reason we have pirates off is because most people don't like the feature. If it's improved, that might change. Worth consideration, at any rate.
stealing income... decreasing ship build time... its a diplomatic ship... not a Sova.

Indeed, although I think this is the right direction to be thinking, these abilities are already unique to a capital ship. Envoys certainly need something, but it needs to be unique to them, not a rip-off of existing abilities.
i am always surprised that only 5% try online, thats pretty sad that people buy the game and don't explore it to its full benefit.
It's true; as much as online gamers are well represented on forums, in terms of the player base we're a tiny minority. Doesn't mean we shouldn't have some goodies to play with, but we gotta keep that in mind.