User blog comment:Crimson and Darkness/Shin DxD 3 discussion/@comment-105.186.247.21-20190821060657/@comment-36523287-20190821071114

Rias and Sairaorg have a good chance to be promoted to an ultimate class. Not sure about Sona and Seekvaira as their achievements are less spectacular than other two.

Considering privileges and prestiges of being an ultimate-class devil, though, it's also possible that only Issei will be promoted. It's like when a lot of students in the class who are qualified for grade A, teachers may raise the threshold to ensure that only the best of them actually receive grade A. It's a policy to prevent grade inflation.