I saw some really awesome suggestions in here on the first few posts and I would have to echo their sentiments.
Death and Debauchery:
Lords, whether great or small, chivalrous or dreadful, good or maligned, are human.
Sex is something I would like to see in this game. Not in the form of a literal game mechanic or experience that the play actively participates in. But as a tool for political motivation. Such as gathering heirs, or making bastards, or pursuing the interest of some high lord's beautiful wife who has an eye for you... I have to agree with the user who previously stated this idea... that would be awesome. In general, depth between characters and character interaction would be greatly wanted.
City/Castle building.
If you purchase land in a certain region, you can terraform that land, and build structures, enforce peasants to gather resources, and play an active part in developing your fief and castle to your liking.
Personalizing castles and rooms. Making the home more comfy and immersive. Such as being able to add decorations to your castles as a part of the game itself, and not as a mod creator necessarily. being able to use items like chairs to sit in, beds to sleep in, and being able to interact with your castle staff (who can grow to like you or loathe you), along with your family (be it wife, or the children who live in your house hold. It would be awesome to train with your son in the Castle yard, and teach him the ways of the sword, so that when he comes of age, he will inherit some of your skills, and grow to be a better man than perhaps even you were. And some sort of time shifting mechanic would be awesome.
Say if once you build a floor plan for your castle or certain buildings in your fief, it would feasibly take a year or two to build, you can sit in your settlement, and activate time compression that allows time to pass by months in mere seconds (or until an important faction update or event has occurred that will pop up in a dialogue box. So you don't want to wait for your castle? So be it. You can compress time ahead and fast forward to its completion, where your character is now 3 years older, and you may even physically see them age.
I'd like to see a disease and sickness mechanic. Along with a player stat that increases a player's immunity system. The younger you are, the higher it is. The more fit you are, and the more variety of good food you eat, the higher it is... but over time, as you grow older, your immunity system begins to fail. Eventually, even if you are very healthy and fit, your odds of surviving a severe sickness become impossible, and you then are killed. When you die, you are then allowed to choose the role of any of your successors, You can choose the oldest son, who will then be the Lord of your fief and keep, or you can take control of a younger son or daughter, and you will have no rights or claims to the castle itself upon coming of age, save for the hospitality of your brother (especially if you have a good relationship with them!) It is an open ended choice given to you, to try and start a new journey and make a place for yourself, not necessarily as the Lord of your keep, but a noble of a family that is making their own way.
of course, family is not limited to nobles. If you are a commoner, you can purchase property in cities (such as a home which can vary from poor, middle , and wealthy homes) and you can dote on the common populous. It would be suggested not to try and dote on a noble lord's daughter however, as you will likely be thrown in prison and will have to wait out your days for insulting the Lord.
Anyway. I hope they bring the RPG aspect of the game more to life.
Last suggestion:
Combat.
Nerf the feinting, if there is ever a multiplayer component. 360 degree swing radius. Stamina... stuff that makes the combat more
