If we never get to see Northern Mirkwood, Esgaroth, and Erebor in their entirety, why not add them as Housing Areas?
Nothern Mirkwood Houses could be in Thranduil's Halls. Now as for what the houses could look like, I have no idea. Either the Wine Cellar or Thranduil's Throne could be central areas for the homesteads (the places with vendors and vault people). I think the Wine Cellar would be more ideal for a marketplace, but Thranduil's Throne might be a cooler central area.
Esgaroth could be a very cool place for houses, and could easily have a market area made in the center. Not sure anything else really needs to be said about this.
(Spoilers ahead, you've been warned.)
Erebor would just use normal Dwarf houses, but could include an interior and exterior housing area, interior might feature a central area of Thorin's Tomb (told you). The exterior could be an outer ledge above the gate, overlooking the city of Dale in the distance. (Not sure if Dale could also be a Housing Area? Just a thought.)
Now, I would personally prefer to just have these places released as expansions, which I still hope will happen, but this could make for a nice substitution.