It would appear the tradition continues! Entertainment Weekly has recently posted an exclusive that Sigur Rós will be joining the cast for season 4. According to EW’s article the group members are currently shooting their appearance on the set in Croatia.
In past seasons the series has had bands perform original songs from the books (not necessarily how I imagined them being sung…Bear and the Maiden Fair) such as The National -The Rains of Castamere, and The Hold Steady - The Bear and the Maiden Fair. In season 3 we had our fair share of musical guest stars such as Snow Patrol’s Gary Lightbody, and Coldplay’s drummer Will Champion.
So with that in mind what can expect Sigur Rós’s role in season 4 to be. Possibly just an extra who made it on screen because David and Dan are fans of the band. Or could they be singing a song for a possible upcoming celebration. I would assume they will be putting their musical abilities to use in season 4.