It looks like those rumors of HBO shortening future Game of Thrones seasons are true. Jack Bender, who directed “The Door” and “Blood of My Blood,” stated that he's unsure if he'll direct an episode of the fantasy drama next season because there will be less opportunities. "I don’t know the answer to that," said Bender when asked by Vanity Fair about a possible return. "They’re only doing seven [episodes], and they’ve got their regulars who have done it forever."
With season 6, HBO has officially passed author George R.R. Martin as the latter was unable to finish the sixth volume The Winds of Winter before the current season's premiere. Martin supplied showrunners David Benioff and D.B. Weiss are operating with notes from GRRM but a good majority of the remaining storylines will be created in the show's writer's room.
To date, Martin has stated that his Song of Ice and Fire fantasy series will consist of 7 volumes, with the last installment, A Dream of Spring following The Winds of Winter. However, there are already rumblings that there could be an 8th installment. It certainly wouldn't be without precedent as Martin originally conceived A Song of Ice Fire as a trilogy, before expanding to 4 books, then 6 and now 7.