Some suggestions (and sorry for my bad english)
It would be nice to see Rivers in the game. For example there would be ferries, bridges and fords and some of the Houses collect tolls for crossing a bridge, there are bandits at fords, monster (Waterghosts for example the Blutschink from Tyrol) live near the river, you have to fight on the beach against enemies and so on.
2. Mountain Passes
Same idea as Rivers
3. Dynamic environment on the battle screen
A old tree blocking your way? Cut it down and block with it the path of your enemy. Your unit stand a level under a rock? Too bad, the Bandit uses all of his action points to push it and your unit is unconscious for a turn. There is a shrubbery? Put it on fire with a tinderbox, so bowman have a penalty for firing behind the smoke. I think the point is clear.
4. Naval actions
Rent a ship (for a fixed cost or a fixed time), fight pirates (or be one like Störtebeker) and Klabautermänner, find hideouts and stranded ships, fight on ships hire for your mercenaries sailors, trade and so on. Would be a nice addition and would make harbors more interesting.
5. Be a Freeman / an outlaw.
Start with a band of bandits, you can only enter villages at night, but there are independent settlements, you have to find. You only hire people from there and quests, but they need half of the food and are cheap. The Houses hunt you, if you are near, you can sell and buy goods directly from caravans.
Sounds wrong, but as a concept, it would be nice to play the game with some people. One player is the Dungeon Master, who gives Quests, fight the Players and sees the world map without the fog of war and can put some monsters, lairs and so on there. Each player controls to three brothers in the company, recruit them, level them up and gear them. How they separate the loot is their problem.