The final season of Game of Thrones certainly ended with a shocking plot twist after the Iron Throne was destroyed. However, book readers may have noticed that Tyrion Lannister's idea of forming a Great Council where the leaders of each kingdom would choose a new ruler isn't something new. It had been previously suggested by Catelyn Stark in the second A Song of Ice and Fire novel A Clash of Kings.
In A Clash of Kings, one of Catelyn's chapter covered the murder of Renly Baratheon by the smoke demon created by Melisandre. However, it was the exchange between Cat and Renly before disaster struck that would be surprisingly familiar to the show's viewers.
In the chapter, Catelyn tells Renly that the Lannisters tried to kill her son Bran Stark and they could easily reveal the Lannisters as the usurpers since Cersei's children are born of incest. For this to happen, Cat proposed that Robb Stark will set his crown aside if both Renly and his brother Stannis Baratheon do the same. All three could then come together and dethrone Joffrey Baratheon.
"Let the three of you call for a Great Council, such as the realm has not seen for a hundred years. We will send to Winterfell, so Bran may tell his tale and all men may know the Lannisters for the true usurpers. Let the assembled lords of the Seven Kingdoms choose who shall rule them," Cat said to Renly in her chapter.
Interestingly, the scene didn't play out the same way in the show. Instead, Renly told Cat that Robb can continue to rule the North if he joins Renly in the battle against Stannis.
It's a sad thing that Catelyn never got to propose the Great Council in the series. Nevertheless, it still took place and the council chose Bran as the new ruler of Westeros.