Well, we still don't know, what kind of time frame, of Ise's demon life, is going to be portrayed in the novels.
Since, the author did mention somewhere, that adding new members to Ise's, would cause the current heroine's to lose some spotlight, and some of them, still need some quite heavy development of their relationship with Ise, I think that it's going to focus on the girls that are currently in Ise's harem, which is still quite a lot, for any "normal" guy to feel a little jealous - after all, at the current point Ise has got in his harem, Rias, Asia, Akeno, Koneko, Irina , Xenovia, Ravel, Rossweisse and probably Ophis as well
- and each of them, will probably need a lot of screen time, to achieve their happy ending, which is what the author said, he aims for.
Based upon that, I doubt that we will have any new additions to Ise's harem, and even if they are going to be introduced they would probably have some minimal amount of screen time - something similar to one of the Sitri clan girls, which has been mentioned of having a crush on Ise, Kunou, or Abe sempai, who also seemed to have fallen for the MC, and apart from that, there haven't got a lot of screen time, in the main stories plot.