I get it, Nurgle is probably the most popular chaos god, and The great Horned Rat the skaven worship is almost the exactly like Nurgle, so it makes sense for them to ally. Nurgle was also very very active during the end times, his worshipers were some of the first to directly assualt the heart of the empire.
But he’s not the only chaos god. How about some Slaaneshi demonettes, or Khornate berserkers. Hell even some Tzeentch sorcerers would be cool. There’s tons of chaos troops to draw from since the end times was an assualt by Chaos Undivided, not just Nurgle.
When we get dlc maps, please consider adding followers of other Chaos Gods as enemies, not just Nurgle. How cool would it be to fight a Bloodthirster as a boss?