So I noticed how public order was not really an important mechanic in warhammer 3. Maybe this could be interesting:

-Each negative point of public order provides a 0.1% chance of causing sabotage (building damage) in the settlement each turn. (As a form of riots)

so -50 public order provides a 5% chance each turn for buildings to blow up

Could be cool? Reward players for having positive public order and make negative public order more noticeable?

Also a short list from my other post:

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The administration feature that comes with Pharao is a pretty good way to reduce lategame snowballing 

Per settlement a faction owns, they gain:

+1% extra movement during forced march. (to move around the empire faster)

+0.1 global recruitment slots. (to reduce recruitment waiting time)

I also really like the labour mechanic for Pharao, meaning building any building requires growth, it simply adds more thinking to planning city expansion and makes growth more valuable.

I also hope that some idea's from Shogun 2 return, such as making buildings locked behind technologies, thereby making the technology tree not only provide campaign buffs, but also major strategic city development considerations.

Reducing income or increasing upkeep for all units might also be a good idea to reduce army spamming that becomes a real issue. Or having armies cost +250 gold for each army you have, to incentivise building elite armies over spamming flexible armies. (so 1 army is +250, 2 armies is +1000, 3 armies is +2250)

I'd like more military leaders to have governor traits which apply to the entire province, so many traits currently only apply to the current region and are simply not big enough to incentivize keeping an army that costs 3-6 provinces of upkeep in a region a turn longer than movement/replenishment forces them to remain. 

The main way to make that work is with public order and influence where Dynasties did a much better job balancing that than most other TWs. 

Newly conquered regions should not be profitable in 1-2 turns as they are in most TWs, even more important, not reach max profitability in less than 10 turns in most cases. 

Having an army remain as a bonus to public order is included as a mechanic but since public order has minimal impact to output in most TW games, why bother?

Then the question of influence which I think is nearly as important as public order for recruitment and upkeep costs. 

I'd divide public order and influence thusly;

Public Order affects how efficient infrastructure is, with the % of public order corresponding directly to efficiency. If Public order is at 50% then buildings are only producing 50% income, if replenishment of an army is normally 10% then it would be 5% with 50% public order. Construction costs would be inverse to public order, 100% public order = -50% construction costs but 0% public order = +100% construction costs. 

Influence would matter for how quickly public order can increase while it slows public order decreases. Separately higher influence increases recruitment slots and lowers recruitment costs and max influence adds low-tier garrison units for extra defences. 

Attacking core lands should be more difficult but lands which have frequently changed hands or are along a border with various areas of influence that lower the max influence to 60% or so are slightly easier to attack. Not talking huge differences, Max influence could add 2 low-tier melee and 1 low-tier ranged. Influence between 40-80 adds only a single low-tier melee, while anything below 40 adds nothing. 

"Newly conquered regions should not be profitable in 1-2 turns as they are in most TWs, even more important, not reach max profitability in less than 10 turns in most cases. 

Having an army remain as a bonus to public order is included as a mechanic but since public order has minimal impact to output in most TW games, why bother?"

having public order scale income from a settlement does sound pretty cool imo

great idea