Sequels/prequels are closer to becoming a reality. HBO announces they have hired 4 writers to explore different time periods of the Game of Thrones universe and submit scripts for spin offs:
http://money.cnn.com/2017/05/04/medi...hbo/index.html
No guarantee that a series actually comes out of it. And not really a surprise as HBO is obviously not going to let this cash cow just die without milking every drop.
Weiss and Benioff (showrunners for the main series) and Martin will be attached as executive producers.