TL;DR: Major Settlement Chaos Portals.
This probably isn't the first time this idea have been presented, but I think it's worth considering. Here's the idea:
Major settlements razed by Warriors of Chaos are transformed into a Chaos Portal.
Minor settlements can stay like they are today.
Chaos Portals (razed major settlements) have levels, 1-5, like normal major settlements. They start at 1, and gradually level up over time. Every time it levels up, it spawns an army with an army strength based on the portal level. For example:
Level 1: Beastmen small army. (10 units?)
Level 2: Beastmen medium army. (15 units? Medium tiers.)
Level 3: Warriors of Chaos mid-tier army/ Full Beastmen armies with more monsters.
Level 4: Warriors of Chaos army(Mix of medium-high tier units)
Level 5: Warriors of Chaos army. (Max tier units only: chosen, giants, chaos knights, dragon ogres...)
The new chaos invasion setting could be used to set how fast these portals grow.
So in effect; the first turn after a major settlement is razed and the portal is created, a small beastmen army will appear and go raid some ****.
10 turns later, the portal will have leveled to 2, and spawn a bigger army. Repeat.
On max level, 5, maybe the portal can keep spawning an army every 10 turns. (or every 12, 15, or 20 turns.)
Chaos portal growth speed can be tied to Corruption in that area. 100% corruption = 100% speed. Lowering the corruption will make the portals grow slower, or completely halt their growth and spawn rate.
Possible additions and limitations:
- There could be a limit to how many armies the Warriors of Chaos faction can field using the portals.
- Chaos portals could destabilize over time after reaching level 5. Maybe every turn after level 5 there's a 5-10% chance it falls completely apart, or resets to level 1. This could be a countermeasure against a potential snowball effect. So we don't have 10 doomstacks spawning every turn from turn 200.
- Archaon could have a global negative effect on all Chaos Portals when he is killed. Maybe they level down -1 level, or crumble if they're already level 1.
- Corruption could be a requisite for spawning armies and portal growth. We could make the portal require at least 25% or 50% chaos corruption in order to grow and spawn armies.
- Growth speed of Portals can be tied to the level of chaos corruption in the area. This will reward players for fighting corruption, and provide an alternative way of stalling the growth of a portal if the player is busy with other troubles.
I think this will make the emergence of chaos more dynamic and interesting. It will incentivize scouting for portals, and mobilizing to shut down portals before they grow too strong.
Instead of the invasion being one giant blob of HP going north->south, the map can change more dynamically.
If a wave of chaos buzzsaws through the empire, instead of gradually running out of HP and units, it could make a portal at Akendorf, or Karaz-a-Karak. Or maybe even in the desert if it makes it down there. As the empire re-settles its razed cities, there's now a portal to the south, or west, or east. This makes map awareness more important, and can encourage the usage of various chokepoints and forts that are usually never used. It also makes corruption more important to pay attention to.
I hope this idea finds you well. Please share your thoughts, concerns, and stuff. I don't think this is too difficult to implement. It would be nice if it included a few Chaos Portal maps, with no walls, some ruined buildings, and a portal in the background.
PS: I've tried mods that do something like this, but they all made my game crash from time to time, or they neve worked. So I'm hoping CA can implement something like this to make the invasion more fun. Because in it's current state, the invasion is more like work and less like play.