The lights flashed. The bass kicked in. The crowd went wild as a cast of dancers peeled off to reveal seven figures on stage against the backdrop of Seoul’s Gyeongbokgung Palace. It was the comeback concert for BTS, perhaps the most famous boy band in the world. But their much-heralded return in March, nearly four years after they went on hiatus for mandatory military service, has also highlighted a key question for the K-pop industry: What comes next? The genre looks completely different from when BTS first debuted in 2013. No longer is K-pop a fringe or novel concept; now,...