Few fast suggestions (DANGER - bad english detected):
1.Option to change player/player faction lords party's models (on the map, You know, like these from new factions)
2.Moooore banners
3.Multiple mercenary units in tavern (i.e. 2)
4.Speak to village elder option
5.Following cattle
6.Military academy building where you can upgrade units without xp (only for gold), but only specific amount of soldiers per month
7.Bandits and patrols able to take lords as prisoners
8.Bandit armies with ability to plunder villages (and maybe taking castles/towns)
9.More bandit types and bandit troop trees to make them stronger
10.Much more towns, castles and villages on map - it looks really empty
11.More special locations too
12.Ammunition packs for long battles and sieges (auto-use after certain time period)
13.More diversity in armors and weapons (for new factions and vanilla ones)
14.More Berembert's inventions
15.Maybe some alchemy system with i.e. potions giving better skills for battle (manually or auto-use) for player and companions (auto), and some from really rare ingredients giving +10 to certain proficiency or +1 attribute/skill point
16.Single mercenaries in castles/villages/town centers
17.More minor factions.
18.Stone club/hammer for stone golem and copper spear/shield for clay golem to get a better color match - but I think it's just my litttle perversion
Edit:
19.Possibility to end mercenary contract by speaking with king (just realised there isn't that option)
20.Option to set amount of reinforcement waves during battle (hate to enter 20 battles to win one big)
21.Bigger "in the streets" battles
Edit2:
22. So, if mercenaries will do everything for money, they shouldn't be affected by Undead, but they could get "undead company compensation" i.e. 50-0 denars per mercenary unit (50- 0 leadership, 0- 10 leadership)