Hi and congratulation with all the work you accomplished with this mod, considering the small team working on it.
This a brainstorm thread so i guess i will not be flayed if i throw some idea in from my chaotic mind.
Personaly, i think chaos should not be a playable civ.
Indeed chaos dont own land, it just occup the land where he is. Chaos is basically the antithesis of order, planing and organisation (the things that make real civilisation) so i don't see chaos owning city and building farms and plantation with his workers. Moreover if chaos is a civilisation it can be destroyed like others civs.
Chaos is the great enemy of the world of warhammer,an aglomerate of concepts and emotions that extand like a cancer with nothing capable of stoping or killing his essence. It is not a physical political entity that can be bribed with diplomacy or invaded, and last but not least: No chaos= No magic.
But chaos can be represented in the civs who bow to him:
_The Kurgans with his countless tribes and fierce warriors (the ones who make the bulk of each chaos invasion)
_The Hungs (like kurgans in power but with hordes of mounted warriors)
_The norse (with their bersekers devoted to khorne they allowed archaon to take Erengrad)
(Remove the Ungol or make them a barbarian city, they were a minor tribe and where assimilated by kislev long long ago)
Indeed there is no Odin, thor or wathever in warhammer, the kurgans, the hungs and the norse worship Khorne, Nieglen (nurgle), Loesh (slaanesh) and Tchar (Tzeentch), a myriad of their ancestors who ascended to demonhood and twisted aspects of the gods of empire (like the creature from the deep "Mermedus", venerated by the Skaeling tribe as an evil aspect of Manaan).
These 3 tribes should be able to build shrines to particular chaos god (one temple per city) to have access to demons and chaos warriors.
A thing that would be really cool is making chaos a civilisation that is not representated physically:
At the begining of the game the Chaos portal is created by the barbarian at the northern pole. This "chaos portal" will act as a sort of ONU of the vanilla game but only for the civ who have Chaos as their state religion. This "onu" ask the chaos civs to do certain things like :"We command you to raze middenheim city".
The chaos civ who accomplish the thing asked by chaos will be granted with a demon ressource, small chaotic wonder or spell.
This Chaos portal could even give special promotions to chaos civs units who did special things (like killing a priest of sigmar).
There is a countless number of things the chaos can ask like : "build x temple of slaanesh", "attack x civ" (even another chaos civ). "Kill this particular unit", "propage chaos religion here". Even strange things like "build this improvment here" or "destroy this unit you have" .... We are speaking of chaos so logic is not a necessity

.
Moreover the "Chaos portal" destruction could be a winning option (like the spaceshuttle of vanilla).
I have other idea for chaos wind, mutation and chaos waste terrain propagation. Just ask if you are interested.
I know the things i propose must be hard to make but seeing what has been done with fall from heaven, i think it's not impossible.
I wait your comments, thanks.
(I forgot to tell you that the god of the chaos dwarves is Hashut the father of darkness)