I thinking and maybe I have much better idea for Iron Hills:
Maybe movie Iron Hills soldiers and Ram riders could be integrated as Ered Mithrin units for Assembly Hall. So, Iron Hills units will have old edain design(Iron Hills dwarves from book) and Ered Mithrin will have design of Iron Hills dwarves from movie.
Maybe second Iron Hills army of Ram riders is from Ered Mithrin(Ram is here symbol for Ered Mithrin):
Also, Dain can have new spell on level 10:
Reinforcements from Ered MithrinDain summon only temporarily reinforcements from Ered Mithrin.
Dain on foot: 2-3 battalions of infantry from Ered Mithrin
Dain on boar: 2-3 battalions of Ram riders
So, you can get this movie units without outpost.
And hero unit "Veterans from the Battle of Five Armies" can have this design:
What do you think about this idea?