My bet is Atlanta for the following reason:
Atlanta during W19 will be served 5x weekly by a 4 class 777 and 2x weekly by a 787-9. However, from 1st February it changes to a daily 787-9 service. Given the 787-10 is expected in January that seems like a sensible time for them to pencil in 787-10 flights and also it’s not hard to change the equipment from a -9 to -10 at short notice.