This idea looks like it has some merit now...So I'll throw a few ideas at you:
Daemononic Minions formation- Use current stats, daemonic champion/herald as leader upgrade, GD and DP maybe as upgrades, chaos spawn and daemonic beasts as upgrades with maybe soul grinder as well? Keep singular god formations due to rivalry
Daemonic beasts Packs- Again current stats, they work so why change them?
Avatar of Chaos formation- uber god-specific avatar (think bigger GD) with a coterie of GD's or DP's, you know you want to...
Daemon Engine formation- Using soul grinders as 'basic' unit, with one or 2 upgrades? Maybe a larger engine as a 'leader beast'? or a flak unit?
Get formations of all of the god specific daemon engines in for varietys sake as they are all daemon engines
For titans, I would go only a reaver or warlord size class titan and alter it considerably under the guise of a "daemon titan"
Chaos spawn packs
Gargantuan chaos spawn? Either as a war engine or a chaos spawn pack upgrade
Chaos altar, similar in vein to the LoTD one
Definetelly get Aether Sharks in there, but keep them limited
Rules wise:
Whole army teleport? Similar in vein to the 40k rules, but keep strategy rating low to counter this
Initiative 1+ with maybe -1 if within 15/30cm (?) of a another god's formation to represent bickering?
Huge variery of units (as above)
Keep Anti-air as a distinct weakness IMHO, and the maybe one titan class as the GD are effectivelly small titans, as well as the larger daemon engines such as plague towers, warp palaces, lord of battles etc...
Feel free to tell me I'm a fool but it felt nice writing that

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