Maby you can try add custom heraldry(banner making), like in: "Rządy Miecza" (Reign of the Sword) - info on first page http://forums.taleworlds.com/index.php/topic,56748.0.html
... and I think you can change faction name ... will be nice if we see reall faction, like:Fleming, Brandenburg etc. (your chose). Create some reall banners. With "custom heraldry" this can be good.
... add recruitable lords.
... some unique epic items. If we win with "king's party",finish hard quest or somthing ...
... maby some unique mercenary troops, whos we can recruit if we have high reputation.
... tournaments? This will be ok, winner gets epic items and reputation.