Things seem to move at a faster pace with each passing chapter. Already we have 4 bankai-less captains in one week. Also, I'm so curious to see when Kenpachi will finally enter the stage. I would't be surprised if he ends up taking down a couple of high-level SR all by himself. Would definitely be something his fanbase would masturbate over for months.
The fact that their Bankais were stolen is different from the fact that their bankai was sealed. If it was sealed then they would be in the same situation they started off with. But since its stolen, now it means that its in the hands of the sternritters so its possible that their bankais will be used against them. I hate those clusterf*ck characters like Arienaro because they aren't individuals or special characters. They're unoriginal. In a manga like Kubo's where specific powers=personality it would be really lazy for him to have a certain character copy another character's power in any way. It basically reduces that character to a talking plot device.
I was thinking back to the Zanpakutou Arc and the information that came out around the same time that Kubo had retained control over the design of the zanpakutou spirits in the anime because he was thinking of using them later on in the manga.