Other people have probably said this as well but it would be pretty cool if Eshin's unique mechanic was added as well (minus the part about other clans relations), and if you needed to confederate with the other factions first before being able to use their mechanics.
Also this concept would be cool for other races too if you feel like making mods for them, like lizardmen with Cult of Sotek or High Elves with Imrik's dragons and Yvresse's system

I always wanted a mod like this. If you ever want to expand it, I'd suggest allowing other skaven lords to use the special under empire buildings of pestilens and skryre, the plague cauldron and doomsphere

Hey, Queek Headtaker fan, it would be neat to see if he could get the Flesh Lab. Some of the upgrades you can give through Throt are amazing.