I think there should be a mechanic where you can Confederate between HE,WE and DE. And form 1 single banner elven kingdom.
Lore-wise it should. And would be epic too see. I hope they can integrate it on Warhammer 3 or so. Since it might really suit the thematic 'End times' of the Warhammer world.
Nothing more epic than seeing all your past enemies working together facing the Entire force of chaos with 60 stacks against 10 allied confederation stack.