Well the bold now that you mention it seems the most plausible. They were practically giving off fear of both of Unohana, and Kenpachi. Wouldn't be surprised if to counter her possible power, they gave the ultimatum To Unohana, leave SS or do something that reduces your power.
Think this kind of brings Kenpachi's eyepatch into a whole new light! He says he asked for it and no doubt he did, but just imagine behind the scenes they were possibly preparing that and more as a just in case.
Wouldn't be so sure on the underlined. There's many possible reasons that would encourage explaining in later 'flashback' chapters, and possibly derived situations, which might seem the path Tite Kubo might want to go.
For 1 example If they're afraid of Zaraki then they also probably feared the 1st Kenpachi, even possibly now, so why give her total absolute power just about that easily. For another example, Unohana's been healing for a while, maybe they think she's no longer at that level worthy( they being the central 46).