There's my COE summons mod over here. Sombre's summons mod also uses graphics from coe3. COE is largely generic fantasy stuff and there's a lot of overlap with graphics from dom3, so there's not much room for nations. There are some dwarf graphics that someone could make a nation from though. Brainpipe isn't an illwinter game, it's some other thing that shrapnel also publish.
As far as CoE3, CoE3 has more updated graphics that Dom3 can use but less content for nations. So its more useful as a way to upgrade images in dom3 or add some interesting summons.
On the other hand there is a huge territory to port nations and other things from Dom3 to CoE3. There are some modded nations also for Dom3 that I would love to see ported over.