Look at the ToDo list, if i'm correct this is already therewhat about making the rohan heroes buildable from the golden hall.. so you can completly forget your ''normal'' castle en just focus on rohan units and buildings?
And i don't know if it's in the game already, but IMO Boromir, Faramir, Pippin, Merry, Aragorn should have skin changes and armor bonus as they level.
For example Aragorn:
lvl 1: strider outfit
lvl 3: normal outfit
lvl 5:Helm's Deep battle outfit
lvl 8:Black Gate march outfit
lvl 10: Coronation outfit
Boromir, Faramir, Pippin and Merry:
lvl 5:Armored outfit
yeah i agree, this would bring more diversity in the heroes... without actually adding heroes..