We have our advisors, we have the Witch, and we have NPC Kingdoms. But there's so many other opportunities for NPCs that could give us new goals and gameplay mechanics. Here's a few of my own ideas;

Head Mason that we can support to prioritize maintenance tasks (such as focusing on castle walls and roads primarily, and leaving production structures after).

Theater Troupe Director that requests funding for new material. Sort of a home grown of the NPC Kingdom play event, but you can actively make a selection to which plays you permit within your Kingdom, thus controlling the Happiness output from your peasants. Maybe make Peasants grow bored of certain productions with time, causing a need to switch things up every few years.

Union reps that could improve various businesses, but each improvement tacks on a maintenance charge to keep the improvement running. Blacksmiths could improve production speed. Bakers, Butchers and Fishmongers could increase effectiveness of turn out per resource. Markets, Graineries, Stockyards and Docks could improve total storage capacity. There's probably more that could be done here, but these are what I can think of off the top of my head.

Clergy that could provide blessings based on total Tithe paid (increase chance of free smite on enemies, reduce hunger in peasants for a time, increase yield from mines and quarries for a time, etc).

Maybe further improvements could be made for our Advisors and the Witch. Maybe make the Witch part of the advisement team by turning her hut into a building that you can actively place down like the Chamber of War? The military advisor could improve troop and defense structure capabilities with certain quest lines fulfilled. The agricultural minister might help improve soil conditions or farm/orchard output with his own quests. The city administrator might improve building happiness range, or make improvements to houses to increase their storage and decrease their food/coal consumption.