Although the forces of country music are waiting for BTS' return to deliver a decisive defeat, and Taylor Swift and others are going to contribute for it as well, at least its initial return concert, probably to be held in Korea, will be big.
The infamous Chamshil Olympic Stadium, after long delays, is finally being renovated, to be finished sometime in late 2026, which in Korean lingo means sometime in the first half of 2027.
In Japan, the highest stadium is the National Stadium in Tokyo. Only one act , Japanese only, is allowed a concert per year ; before its previous iteration closed down in 2014 only these acts did concerts there - SMAP, Dreams Come True, Arashi, L'Arc En Ciel, Momoiro Clover Z, AKB48 and a joint concert of L'Arc En Ciel, Perfume, Man with a Mission and Sekai no Owari at its closing. Its top capacity was 70,000 but its present iteration has a top capacity of perhaps 65,000.
The Nissan Stadium in Yokohama , the largest stadium in Japan, allowed these acts there - B'zs, Mr. Children, Southern All Stars, SMAP, Momoiro Clover Z, Exile, Yazawa Eikichi (the equivalent to Bruce Springsteen in Japan), Glay, LArc En Ciel, Yuzu, Sekai no Owari, Fukuyama Masaharu, X Japan, Bump of Chicken and Nogizaka 46 had concerts for at least 2 times. DBSK is the only non-Japanese act which had a multi day concert there since it has a capacity of 70,000 - 75,000.
No female soloist, and only one foreign act (from nearby Korea) were allowed into the largest stadiums in Japan.
Koreans sometimes use the world "Moo-geunbon" or "No-geunbon", which basically mean the same thing. Geunbon means "Roots" in the literal meaning but it also means Tradition, Basis, and other stuff regarding an established principle.
Koreans lived dirt poor and they were even poorer after the Korean War destroyed about 80% of all of its territories so a lot of Korean stuff were done without any concern about its basis, like 1960s and 1970s Korean Pop which borrowed freely from American, Japanese and European sources.
The Japanese only allowed acts who were established and had completed the 5 dome tours (including Sapporo in Hokkaido, which is in a cold area so has fewer population so its dome concert is much harder to fill) to have concerts in the highest venues, and just one foreigner (DBSK) after they were touring Japan for more than 10 years. No Yonezu Kenshi, or others they do not deem to be capable enough.
Koreans took everyone who applied, so the first acts who performed in the largest stadiums were actually foreign acts like Michael Jackson, Stevie Wonder, Elton John, Paul McCartney, Lady Gaga, etc all the way to ColdPlay and the recent Bruno Mars.
A lot of Korean events there were one day affairs which didn't sell. Meaning The city of Seoul, who oversees events there, approved anyone without really going over the potential that they could fill the 45,000 capacity Onstadium.
Only 4 acts had a multi day concert with the full capacity. Cho Yongpil (2010), HOT (2017), BTS (2019, 3 days) and someone who should not have been allowed in the stadium because she lacked any capacity to sell venues outside of Korea (2022).
So, out of the active acts now, only BTS and Someone who Should Not Have Been Allowed in the Stadium to Begin With had a full capcity multi day concert in the highest venue of Korea.
I think that for BTS' return concert in 2026, the main stadium won't be available and the Sang'am stadium, as seen in the recent emergency jamboree concert, showed its limitations (it can hold even less people than the main stadium and the Korean soccer fans complain like hell because concerts supposedly hurt the lawn there, not that any person in general is too interest in the Korean soccer league).
So it will have to be an empty space which can fill more than 50,000, and probably 100,000 plus, people who will attend BTS' comeback concert from all 7 continents since Korea lacks a venue to put more than 45,000 in. Most likely some airport, and for that event all flights for that facility will have to stop.
(The CJ arena has suspended construction because CJ is not doing well in its main business.)
With an older generation which has no concern over KPop running the country, and a populace which cannot tolerate the sacrifices needed to make KPop Supreme in the world and does not lose any chance to undermine it, finding a place for BTS' return concert might be hard and they might have to fly to some other country to do it, leaving Korea as the last destination.
The only hope to remedy this situation would be using the Nungrado Stadium in Pyongyang, North Korea, with 150,000 capacity (although it completely lacks any amenity), could be put in action. It might be necessary to ask whoever would be ruling NK for permission to use it, which is probably going to be granted providing the ruler to be one of the attendees.
Unlike the Japanese policy of allowing concerts in the highest venues to only established acts and preferably to domestic acts only, the Korean practice of allowing the highest venue to anyone who could pay, including someone who is completely irrelevant outside of Korea, made BTS share the record of someone who filled the largest stadium in the country for multi days with someone who should never have been allowed to the highest stadium in the country to begin with.