Napoleonic Wars added in many things that made multiplayer mount and blade shine. I hope Bannerlord capitalizes on some of those features.
Spears sucked in Warband. Make them more like a musket bayonet from NW.
Add in special troop types like flag bearers and a sergeant/captain of each unit type. E.g Archer, Infantry and Cavalry. There could also be a musician type class for each of them. E.g War drummers, War horns and whatever else they used back then. These should all give buffs to surrounding troops.
These also tie into the above category, but have a playable leader as well. So if this was taking place back in Warband era, you could play as King Ragnar if you were on the Nords team. Have a (sappper) engineer class that can build defensive fortifications. Also a seperate class that can operate the catapults and ballista for better balance.
Naval battles would also be much appreciated.