I remember for ages people have been asking for certain features to be added by default? some are available by mods but their is always a chance that moder could stop supporting it and it becomes useless. Some that I would like to see are:
Refuse diplomacy at the end of turn- When you click end turn and have no intention of signing any diplomatic treaties, click this and the AI will not disturb you until your next turn begins.
Respec your character - Ability to reset skill points and reassign them to your hero or lord
View undercities - Currently if you are playing as Skaven your undercities do not appear in the settlements tab (and the with vampire coast with vampire coves). So they should appear in this settlement tab as well. As it is at the moment you have to look all over the map and its easy to lose track of one of them.
Are there any other mods or features you can think of you would like to see implemented in WH3?
Obviously I have not mentioned the diplomacy rework and region trading as I expect they are doing that already.