This topic seems to come up every other week in this thread.
Many of the quincy alphabet people are not accounted for. Chad and Orihime are with Grimmjow in Hueco Mundo; Nel and Haribel are still there as well. The 3 stronger fullbringers are with cousin Shiba. Many of the other captains have only had speaking roles at the very beginning of the arc and have never shown bankai; other captains are recovering from their first battles and will be back (ice boy/dog man). Several other lieutenants are supposed to bankai (shuhei/already saw rukia and renji's new stuff). The Kisuke/Isshin/Yioroichi/Tessai group is doing something. Aizen.
Everyone will have to make an appearance and there is a lot left to showcase. At the pace Kubo is going there are at least another 2 years of combat alone - chapter after chapter focusing on their fruits of labor from the training during the time skip. Lots of "Here's my new ability!" and "Ow, your new ability is killing me!" for months. Everyone has enjoyed the return of Ken, but I've definitely enjoyed how Naruto is culminating more than what's becoming of Bleach.
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