Originally only GD and YB were supposed to enlist next year but Daesung and Seungri decided to go a bit earlier than they need to in order..
— 수사나 (@susifg) September 21, 2017
Multiple Japanese media outlets have reported that the rest of the Big Bang members will be enlisting next year.
According to outlets such as Sankei Sports and Daily Sports, G-Dragon and Taeyang already plan to enlist next year in the spring. While Daesung and Seungri have some time left before the deadline, they’ve decided to enlist along with the older members so Big Bang can come back to fans as a group as early as possible.
This may have some weight, as during Daesung’s August concert in Japan, he told fans, “When I am done with promotions this year, I might have a long hiatus. But I think it’s the best choice for Big Bang to have a new start.”
Source: ALLKPop and SUSIFG