Back before Total Warhammer 3 released, there was a fanfiction I liked by that title, about Khazrak One-Eye trying to stop the End Times, and I always thought it would make a neat mod.

The gist of it is, Khazrak still wants to tear down civilization, but he doesn't want the world destroyed, he just wants it in a hunter vs hunted, 'nature red in tooth and claw' state. He is aided in this by Drycha, as their goals overlap somewhat.

The mod would alter Khazrak's faction to be Untainted, instead of chaotic. This would prevent them from accessing any units that are 'too chaotic', meaning no Bray-Shamans, no Chaos Spawn, no Tzaangors etc. (Cygors are permitted, due to one of the fic's battles relying on them).

The tradeoff is that, due to Khazrak's alliance with Drycha, he would have access to Branchwraiths and a limited selection of Tree Spirit units.

Naturally, Khazrak would have a diplomacy penalty to all Chaos factions, and a bonus to Drycha.