Even though Warband is an awesome game for me, I've always felt like the whole Calradian lore becomes dull and repetitive over time - taverns are boring, NPCs behave as statues, the streets are devoid of life. Nothing happens, it feels like everything is kind of "dead".
In this installment of the series I'd love to see NPCs behaving as they should be, doing their chores, working, etc. Dialogues to be far more inmersive and not a shopping list to go over again and again. More opportunities as well for players owning fiefs, building certain buildings should not only bring a scripted bonus but as well some lore. A watch tower you recently built that makes the village harder to raid, but it can now act as a tiny garrison for troops as well which will be available in case of a battle. If you build a mill, the new building should appear in the village, perhaps storage boxes to keep some food there as well which you can attempt to steal.
When you visit a castle and the lord is there, he appears at the courtyard training the troops. You can ask to spar with him, or to train the troops yourself. At night he goes inside to have dinner. An advanced behaviour cycle NPCs follow similar to games like Skyrim.
Being able to customise your troops, invent troops, set gear between several options for each tier and troop tree. Fully customise your kingdom, I liked how in Sword of Damocles you could choose a religion. I also liked how random events happen, making the game way more interesting.
Make the persuade skill more useful, add persuasive rolls to conversations just like in games such as Knights of the Old Republic. Removing the relationship with lords for a more complex social system. In warband it seems you had to do this this and that, and then the lord would do whatever you want.
Quests. More quests. We'd love to see countless quests. So many different types of quests that your journal would explode.
Overall being imaginative, this is by far one of the games with most potential. The posibilities are so wide I'm enthralled with this project.