I tried a nakai campaign a few months ago, thinking that having allied settlements
instead of ruins would stop that whack-a mole gameplay of Hordes campagin and make Hordes more fun.
It did. But somehow it was worse. By converting enemy settlements into allied settlements you just create
an empire on auto-run. None of that nailbiting last-stand experience of Hordes, none of the nation building
and strategical decisions of Settlement Factions.
I think the solution lies in the middle.
Hordes should be able to take over settlements by spending Growth points
Thus you have to decide whether you want to update your Horde right now or create a save haven.
That taken over settlement should also belong to you, not some Allies. It can work as a save spot
from where you can respawn if all your Hordes are wiped out. Again, strategic decision making.
Also there should be Landmarks for Hordes. Like the "Blackened Flame of Ulric" in Middenheim for Chaos.
I have not put much thought in the precise math. It should be really high cost.
The decision to create a settlement should not be an easy one.
Also maybe Chaos settlements don' t grow so you have to decide the Tier
with the amount of Growth points you spend in creation.