Durin VII is "the Last", according to the genealogical chart Gimli sketched for Elessar. He strikes me as an apocalyptic figure for the Dwarves - one who is prophesied to come at the 'end of time', as it were. As such, having him in the mod would be somewhat restrictive.
The Assembly of the Seven Houses allows the Dwarves to see an increase in trade income across their realm, and IIRC gives the Dwarf-king some extra Authority. I'm not sure if these effects are all implemented yet, but the building description does hint at what it does, and you could check out EDB for the details if you're feeling adventurous.
As for the eastern Dwarves, they are represented, if in a quite abstract way, in that Assembly building, which simulates representatives from all over converging at Gundabad. Ered Rhun does allow for some... interesting recruitment options (not necessarily the eastern kindreds, but interesting nonetheless).