User blog comment:Rushawn Mclean/captain's bankai/@comment-1906999-20100904182439

This probably won't have any significance in the story, but that is an interesting coincidence. All of the current day captains that were also captains 100 years ago are the only ones who haven't shown their bankai's, with the exception of Aizen. (And Kenpachi, but he doesn't really count in the discussion)

Yamamoto, Unohana, Kyoraku, and Ukitake - All captains during TBtP, and none have shown their bankai Soifon, Gin, Byakuya, Komamura, Tousen, Hitsuguya, and Mayuri - None were captain during TBtP, and all have shown their bankai

Like I said, I really doubt that it's of significance, since many of the bankais were just recently shown, but that is a neat coincidence.