User blog comment:B214/Question and Answers 2/@comment-71.108.89.172-20140203083513/@comment-1359322-20140203155235

Except Rias and the others will move on to Kuoh College, so there's no emotional farewell thing, though it is true that they won't be able to stay close as a group like they previously do.

As to DxD appearing, Ishibumi said that the entire DxD won't appear together as a group, so i guess those appearances are going to be very little to none at all.

Hmm, how will their relationship deepen. Not sure, Ross' one is easy cause she just has to fall in love with Issei. Xenovia and Irina are pretty much in love with Issei already so maybe Ishibumi might move their relationship to the level of the first four girls, it's quite clear that Rias, Asia, Akeno and Koneko have a better standing over the other girls when it comes to their relationship with Issei.

As to new girls falling in love with Issei, probably there won't be any for a while. Well won't it be better after Issei's relationship with Kuroka and Le Fay gets upgraded. :)

Also i think Ishibumi is also trying to make use this period to improve relationship for the other guys. Like in Volume 16, it's Gasper, then for Volume 17, it's Kiba and Tsubaki.