User blog comment:B214/Volume 23 discussion blog/@comment-31137559-20170321042248/@comment-73.160.58.215-20170321231019

Um...I'm pretty sure that they would have to actually want to be promoted to high-class Devils  (which essentially means going independent). Out of all the ones I'm aware of, the only two who might desire a high-class promotion are Rossweisse and Xenovia (and that's a big IF). As for anyone becoming ultimate-class, I'm pretty sure that some rather severe requirements were established. I mean other than the four Satans and Mephisto, the only ones actually identified as ultimate-class Devils were the top 10 of the Rating Game  (Pro) and half of them were fakes relying on the King pieces (that I recall; Zekram Ball is probably there as well). Of course, Grayfia has Satan-level strength, but she's never identified as ultimate-class. There are very special circumstances surrounding Vali being given that rank, including his heritage, his possession of Albion, and his own accomplishments (note that he'd probably already have been high-class). Rias' personal accomplishments aren't all that many if you think about it, and we don't know much about the other rookies. As for mid-class promotions, plans have already been mentioned for the rest of Rias's peerage, and for Saji and Tsubasa at least from Sona's. (We don't even know the ranks of the Baal and Agares groups)