User blog comment:Mnzombie/Issei's Peerage/@comment-180.247.117.13-20121001023500/@comment-1359322-20121121094509

Sorry to crush your hope but in Volume 13 Afterword, Ishibumi answered the question to your question:

“Will Kunou and other girls that have appeared become Ise’s servant?”

Those girls who are not allowed to become a devil due to their position probably won’t. Kunou is the princess of the youkai faction in the Underworld. There is no way that she can become a devil. But I think they can become his girlfriends even without becoming his servants, you know? There are things like local wives, after all.