I agree that would be great to have different veterans for each faction. However I'm more interested in different background than different look and abilities.
Of the three kingdom only Erebor in known to have sent dwarves to reclaim Khazad Dum, so it doesn't really fit to the lore that every kingdom could do it.
So here some idea for a different background for each kingdom
- Erebor Khaza Dum veterans are the warriors that travelled with Balin and survived to tell the story. Exactly as is it now.
- In the Ered Luin there was two great dwarven cities of old named Nogrod and Belegost. They were rich and powerful cities and Telchar, the greatest dwarven smith of all times was from Nogrod. Unfortunately at the end of the first era both were utterly destroyed. However if you see the map of middle heart in the first and third era, you can see that the places where there was the two cities are still there in the blue mountains. So it would be interesting and lore like if Ered Luin veterans survived some kind of expedition to the ruins of Nogrod or Belegost.
- For Iron Hills there is no place in the lore where they could reasonably have found any mithril; so I was thinking of a different material, like the red steel that the axe of Dain was made of. That could be done by adding a red glowing to the mithril mail and decrease a bit the armor improvement.
Hope you find this interesting!
bye