Having to wait longer than normal for the next season of Game of Thrones is a hard pill for fans to swallow given how the finale of season 6 did an excellent job of setting things up.
We already knew that the last two planned seasons (HBO only have a deal in place for season 7, but it's hard to imagine they won't renew) would be shorter as the series' creators David Benioff and D.B. Weiss had mapped out the time they needed to complete the series from the get go. They've estimated that 13 episodes remain, and now that HBO have confirmed that season 7 will contain 7 episodes and start airing this summer (and not April as with previous seasons) this is now a fact.
Creators and executive producers David Benioff and D.B. Weiss recently recently went on UFC Unfiltered (a podcast with Matt Serra and Jim Norton) and they said the new season would likely start later as filming would start later to allow for more winter-like conditions in places they normally filmed during the summer, early autumn. Iceland, Northern Ireland, and Spain are confirmed as filming locations.