Mark of chaos did Nurgle, I quite enjoyed that game even for all it's flaws.

Bloated Thorgar was quite a delightful hero to drag around.

Woh I like the night lords, but had no idea they were so popular.

For me, when I fight for chaos it's going to be as a word bearer, I always liked their lore an design but when I read the first heretic I knew the were epic.

FOR THE DARK LEGION ~ !

Iron Without

black legion it is you lowly mortals

Word bearers without a doubt bringing the word of Lorgar to all

Living Lightning on the armor? There may as well only be one Legion on Arkohna....

AVE DOMINUS NOX

I don't get this, you have 4 undivided instead of 4 centered.
Why not the favored ones like
Emperor's Children - devotees of Slaanesh
Thousand Sons - devotees of Tzeentch
World Eaters - devotees of Khorne
Death Guard - devotees of Nurgle

I feel these 4 would be better starting choices than 4 undivided chapters, if you want good variety these would be better picks.

I understand they are adding more over time, but I feel these 4 should be the ones implemented first and then the others.