User blog comment:SpookyBoogie27/Light Novel Spoilers/@comment-99.251.124.43-20140206215057

Here are a few thing that we know will happen in volume 17:

1. the Sitri clan will start up their school.

2. the Khaos Brigade will attack it, and try to kidnap Rossweise to use her powers.

3. Sairaorg will fight Grendal.

4. Issei will fight Euclid again, and will mostlikey gain his new powerup.

5. Rias, Akeno, Sona, and Tsubaki will graduate.

and this is just by speculation but I'm preaty sure Saji will get his Balace Breaker.