This isn't bad idea, because Rohan anyway have only one kind of elite units for now. Ad So change is that Hama on 10 level can summon permanent battalions of this Royal units. Adding this to Rohan would make more diversity to Rohan's elite/hero units and also make Rohan stronger and easy able to count pike/archers combo.
I agree, I like this idea about Royal guard on foot like permanent summon.