Regarding my earlier ideas -- yeah, I think it'd be hard for the AI to make use of them. For multi, 'tho, they would tend to either make things easier (e.g. sharing province info without typing hordes of individual Messages, and having it associated with that province) or allowing things that are simply impossible now (free passage).
One simpler, if weird idea for multi would be geographical Messages. For instance, what if somebody could send a message attached to a given province? "I'll be attacking here", "Go ahead, it's yours", et al. Buttons could be used to automatically "type in" (so it could be
) hm, army estimates; province information; maybe sites and dominion report?
A far more extreme Version would allow players to send mostly-transparent map overlays to each other, but that'd require a paint program!) (Or, allow an easy way to export maps/import overlays for sending).