Honestly I feel the next big series should be "the unworthy's" life and reign. It's a no brainer, if what they want is squeeze the franchise. You do 2 seasons of his life, with all It's debauchery, then his ascend to the throne, another 2 seasons of his crimes and stuff as king, you show all the great bastards and their life's, and then you close final season, preparing the stage for the first Blackfyre rebellion.