In modern sports, trade are one of the most important and exciting events during the year. It can shape and change the season of all teams. Players changing teams are some of the biggest events in sports history (Lebron to Miami, Messi to PSG etc...).
WHAT IF KPOP WOULD DO THE SAME ?
Imagine something like : Twice trading some vocal members like Jeongyeon/Mina for Soyeon (Gidle) and Lisa (Bp) to go for a hip hop comeback. It would lead to groups going for extreme change in style and music each comebacks. Fans will never experience repetitive songs as if the music gets boring just trade members for others.
Sometimes during the year, probably at the beginning when there are few comebacks, we would have the offseason, with idols getting traded left & right. Imagine some super teams getting created, like Jungkook, V, Baekhyun, Taemin teaming up for a comeback and everyone calling them the new Beatles etc... People would cry, questioning parity of the kpop world, slandering with Mickey Mouse Award, not my goat... 
Imagine if a super team comes up and massively flop, like idk Taeyeon, Sunmi, IU and Seulgi going massively unsuccessful. The drama if some teams break up abruptly and idols start shading each other publicly. 
If we include idols being able to date each other this could become the greatest reality show ever. 
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