HBO programming chief Casey Bloys reveals that the network isn't actively developing anymore Game of Thrones prequels. At one point, HBO was looking into up to five possible Game of Thrones spinoffs, but they said they would only pursue a spinoff show if they felt the story was good enough, not because they needed to expand the universe.
Game of Thrones has been a heavy hitter for HBO ever since the show premiered in 2011. Since then there have been seven seasons with the eighth coming out next year. It's hard for any network to let go of a show that is bringing them in as much money as Game of Thrones is for HBO but all good things must come to an end. However, HBO isn't completely letting go of the franchise since they are making a prequel which can further explain some of the mysteries Game of Thrones created.
When talking with EW, Bloys confirmed that HBO is only working on the one prequel show - from Jane G0ldman - following the series finale of Game of Thrones. When asked about the spinoff series pitched by Max Bernstein, Bloys commented, "I don’t anticipate any movement on any other prequels until we [see what this one is]". He also explained that the prequel will not film this October as previously rumored, but they will instead be aiming to begin production by early 2019.
The prequel series is said to take place thousands of years before the events that are currently being depicted in Westeros. Based on HBO's official synopsis for the prequel, it will take place during the downfall of the Golden Age of Heroes and center around the mysteries of Westeros and the White Walkers. One Game of Thrones spinoff seems a lot more manageable than five and it's surely a safer bet for HBO.
Some fans may be disappointed by the news of only having one Game of Thrones spinoff released but five seemed a bit excessive. There is only so much that can be done with a show before people get tired of watching it. That being said, HBO could always do smaller miniseries' in between seasons of the prequel much like Disney is doing with the Star Wars sequel trilogy and Star Wars stories. Even though Game of Thrones is coming to an end, the show is still in the midst of its popularity because of the anticipation for the final season.