I'm a little improved my old idea:
Glóin already has an great abilities, so I think Dain is better choice for summon ability.
Now in 4.1.1 is Dain most expensive hero in Erebor. Also, I think that King Dain need something more unique on level 10 than building with units from three dwarven subfactions. These units are available in all dwarves subfactions. I have an idea for something more interesting for him:
King Dain(Erebor)
Level 10: Old Warriors
Dain summon legendary companions of Thorin Oakenshield to the last battle. He summon permanently hero battalion like Black riders.
The hero battalion contains these heroes: Nori, Dori, Bifur, Bofur and Dwalin.
I think rest of the Thorin company probably also defended Erebor against easterlings in book.
Of course, they should have gray/white hairs and beards. Also, they can have Erebor armors and weapons from movie:
Old Warriors abilities:
Level 1: Spear
Bifur throw spear against enemies.
Selected enemy unit or hero gets moderate damage.
Level 3: Thief
Nori is an experienced thief. He steals resources from the selected enemy building.
Level 5: Professional warrior(passive)
Dwalin is professional warrior and inspires dwarves on battlefield.
Nearby dwarven units gets more experience from slain enemies and resistance to fear.
Level 7: Wine
Dori gives the wine his companions. Old warriors will restore half of their health.
Level 10: Bofur's speech
Bofur tired of enemy with his speech.
Nearby enemy units gets -20% armor and -15% speed.
One ability for every character in the battalion. You can have only one battalion in game.
What do you think about this idea?