As a big fan of the lore I mostly enjoy playing in my campaigns in a lorefreindly way.the issue I've made for myself here is that if you go lore friendly, there are no evil world empire builders. Believe me I know this is stupid way to behave for a sandbox game.
Now if you're talking about factions that in the lore want world domination theres the lizardmen, chaos and maybe greenskins. The other factions are mostly content conquering thier own regions or nearby such as naggaroth and ulthuan for DE, worlds edge mountains for dwarfs, or the empire for, well, the empire.
Sadly, chaos is a horde and greenskins dont really fit the dark empire builder you can see in other fantasy settings like sauron.
This leads me to Nagash, the only character I can think of that wants to be an evil dude rulling the world and not destroying it. Even the VC are mostly content with rolling the empire in the lore.
So if only to scratch my itch of having a lore friendly, evil conquer the world playthrough, can we get nagash at some point.