A new world map would require careful pixel terrain work for the different types of gound, but could be doable. It is not just the world map that you could maybe get from somewhere, it would have to be done (what you see in the stuck menu I mean).
An issue I can see is with fiefs, would you give them new names but use current maps? Because making new maps would take tons of work and at this point its probably not worth it, but the change in terrain may be fun.