Inhumans should essentially be a cosmic Game of Thrones, bringing the two most unique aspects of the Inhumans together: the immensely varying philosophies of the Inhumans towards not only humans, but themselves. How the Terrigen Mist should be utilized, the different warring factions (Attilan, Ennilux, Lash's group, etc.). Then you have Attilan's Royal Family drama in and of itself, with Maximus, Black Bolt, and the Unspoken One all vying for the throne.
I really hope they do this in the movie...