This is a rumor circulating among Thai K-pop fans on Twitter. It was said to be originated in Korea in December.
A - Gen 2 group whose song(s) known by the whole nation. The group has been active recently and has confirmed.
B - A group from a top agency. The fastest to confirm.
C - Gen 2.5 group whose contract is close to expiration. Members have been active individually and they are reluctant to join. May not participate.
D - A group under CJ umbrella. Confirmed.
E - A group that has just risen on the chart. This group and B were quickest to confirm.
The production team has called F, a hot rookie, but turned down. Thus, the team is considering 2 or 3 groups whose fames are mainly oversea.
K-netz' guess
A - T-ARA
B - itzy
C - Apink
E - Brave Girls or Laboum
F - IVE, substitution candidates - Dreamcatcher, Everglow or Loona.
*Fromis_9 has parted way with CJ so, Kep1er?