This article run by the Eastday Sports (19 Sep) speculates that most likely Diao will be cut from the final 14 list. Many fans said that Diao Linyu is directly marginalized in the photos, standing so far away from the adjacent teammate, Hu Mingyuan.
Nonetheless, it also points out that Lang team may possibly bring all the 15 players in the family portrait to Japan, with the one not selected to act as a member of officials, helping in training process and so forth, as well as to get the major intense competition atmosphere and pressure from close distance for future personal growth. In the case of Diao, she's still young and has the prospect in future. But again, this is only a speculation or prediction.
Notice that in the family portrait, there's no Lang's good sister, Lai Yawen. Some folks speculate that Xu Yunli who has frequently appeared in the NT training may take over Lai's coaching role soon one day.
As about the participation of Xu Luyao in the NT training, the article mentions that Lang Ping might wish to observe her potential from a close distance under the NT coaching team's guidance before the young player can really be admitted into the NT training... a reserve talent for the future! After all, Xu Luyao can play as the main attacking force but also can take the role of an all-round talent.
EDIT: just read that the BRA team will be traveling to Japan bringing along its 15 players. Therefore it has a good ground for the Eastday Sports article's speculation that the CHN team may possibly bring all the 15 players in the family portrait to Japan, regardless who is being dropped finally.