User blog comment:B214/Light Novel Volume 16 spoilers/@comment-23853100-20131019035942/@comment-5185939-20131019174232

Well, potential additions are; Valerie, Sona, Yasaka, Le Fey, Kiyome, and Bennai. After Rossewie as we know her fate is sealed :D.

As for fighting Rizevim, he'll need to achieve Maoh class power without his Sacred Gear to pull it off.

Maybe develop his ability to transform into a dragon to replace the use of his Sacred Gear so he can become a humanoid dragon (like Grendal I mean, a bipedal one) in order to get a power boost.

Still, he'll need to be Ultimate Class in his normal form before it has a chance. Maybe aquire another god-class weapon.