I end up talking about this a lot to friends and family, but I knew in my gut that BTS would have a big impact on Western audiences.
K-pop and Hallyu culture originally drew its influences from Japanese media, as the closest and largest media brand of the day. Although there were also influences from groups like ABBA, The Backstreet Boys and Nsync- the majority of producers, filmmakers, and technicians were trained in Japan. As a result, the terms used in the production field today still resemble Japanese words and Japan and Korea remain huge exports of culture to each other despite rocky politics between them.
Similarly to J-pop today, the early decade k-pop had a specific taste and aesthetic that appealed to only a very niche audience outside of Korea. Just like variety shows and gag jokes, there were many nuanced aspects to the music and branding that just didn't translate to the majority of people in the West. Personally, I began to enjoy k-pop in 2011. Despite the wide-open arms of the k-pop community that exists today, I was labeled as strange, and possibly lesbian based on my interest in Korean media. Listening to anything in another language that wasn't Spanish or French was obnoxious and nerdy at the time.
At the same time, Korea's focus also began to evolve. Korea itself grew stronger and participated much more on an international scale. The collective English ability and interest in the USA or Europe began to grow. Cultural aesthetics and inspirations began to shift- political propaganda or campaigns against Japan were on the rise. EXO-K and EXO-M had debuted, as a try at recreating the success of Super-Junior in 2012. Though they had nominal success and a lasting good impression in the Chinese market, the group simmered out relatively early in their career. One of those factors may have been BTS's debut in 2013.
The first single I had come across from BTS was "Hormone War". I instantly fell in love with the comical lyrics and the crossover vibe I got from the group. They not only represented K-pop but also had a distinct hint of the rebellious and "cool" vibe that American hip-hop/pop possessed. The topics in their lyrics also showed a clear contrast from the other k-pop groups of the day. I could instantly tell that they were not simply remakes churned out of SM or YG, and when I checked, of course, they were signed under "Big Hit" an entertainment company I had never heard of before. As listed in the first paragraph of their fandom wiki, "their lyrics often focused on personal and social commentary, touch on the themes of mental health, troubles of school-age youth, loss, the journey towards loving oneself, and individualism." Not that they were the only ones to do this, but K-pop tended to be notoriously frivolous. Korean friends of mine would often proclaim proudly that they did not listen to k-pop for that very reason.
I, on the other hand, had a different proclamation. That BTS would become a top group in no time. It was clear to me that three factors would proliferate BTS in global media.
1) Globalisation / New Wave in Hallyu
It was not only the Koreans who began to incorporate inspirations from different cultures. The US and many other Anglo-Western speaking communities began to be more open to seeing and participating in things from other places. Suddenly, watching things with subtitles and listening to things you don't necessarily understand became more common and accepted. This tied in with BTS's ability to symbolise Korea's new global outlook, and position as a playing world economy meant definitive success for the group.
2) BTS's crossover platform
To go a little further into the globalisation theme, BTS encompassed a good balance between Western and Korean themes. They kept intact the 'pretty' and soft aesthetic of OG k-pop and married it with the rawness and rebellious vibe of Western pop music. Think of how Taylor Swift changed throughout the 2010s and you will have a parallel of what BTS offered to the global market. In a completely opposite approach from our media, K-pop prides itself in the facade, and the image it creates and profits on. "Idol groups" by design are meant to be much more of a show than artists. BTS offers us a happy medium, being talented and invested in their art/music- whilst displaying the airbrushing that Korean media is just so good at.
3) K-pop's already infectious and meticulous attention to detail
Continuing on that note, there is a unifying factor in K-pop: young and old. That is, that K-pop entertainment companies go the extra mile to present perfect packages along with their artists. Apart from the trends of the market, K-pop already had the qualities of virality.
I used to live in Japan and work in Japanese media. One of the things that I found so frustrating and tiring with Japanese media, is that it was always so unattentive to aesthetics, angles or colour-grading. Though they were once a leader in media production and a soft-power giant, one of the reasons I believe them to not command the same power today is this very inability to produce a more perfect or fantastical image.
Another example of when this thought hit me was when I watched an iHeartRadio interview with Taemin from SHINee. Despite being a very relaxed interview at a restaurant, the production quality was frustratingly excellent. I could barely pay attention to the content because I was geeking out at the perfection of the staging, background choice. Even the food they chose was made to match the colour scheme of their shot.
It is that attention to detail and quality in things that come out of Korea that led me to be sure that it would be a group coming out of Korea to really make those waves in our global media scene today.