This would be silly, but not completely impossible:
You could channel a Siri-like interface into a database of GalCiv diplomacy concepts. The AI would catch key phrases in your dialogue box and make assumptions about what to reply. It is, like a chatbot, a conglomeration of preset replies, but with some cleverness and access to stats in-game, it could be fairly convincing and snarky. You would trade the complexity of interpreting verbal speech for that of interpreting misspelled text, but that could be a plus. With proper flavor choices based on stats and status, it would be very entertaining. You could even work in an extensive interactive help system if you really wanted.
All the present diplomatic options could be used as the actual foundation of what you can do, if you don't mind doing an incredibly expensive digital Rube Goldberg reskin of your Diplomacy. It could end up being the costliest, coolest, and least useful DLC every created! Yet another record for Stardock to achieve. 