I would be disappointed, and honestly surprised from what we've seen so far, if they didn't also develop marked improvements in the diplomacy side of things. I don't expect them to reach Crusader Kings level of interactivity and intrigue, but I would like for them to at least match the level of interaction some of the bigger mods for Warband achieved.
They've already shown so many improvements and alterations to the series it would be rather suspect if they didn't improve the non-combat side of things to match.
We already know of stuff like improving settlements, or destroying them, in order to affect the in game economy and power. Plus stuff like gangs in cities and being able to wipe them out or take over their rackets in cities. Those are interesting indirect means of playing the game and to not have other similar options via more traditional diplomacy would feel very suspect.