User blog comment:Xilinoc/Ch. 609 - "A"/@comment-4822693-20141211203350/@comment-1338810-20141212044704

Given Ichibei's (and Kubo's) love of futzing with names, I'm inclined to believe that Shinuchi is not quite the same thing as a Bankai. "Bankai" literally implies that it's a Zanpakuto's final form (even though Byakuya and Komamura are proof that there can be several permutations on a "final" release) and it's therefore the strongest it can be. Meanwhile "Shinuchi" and Ichibei referring to it as an evolved Zanpakuto imply that a Zanpakuto can go much further than a first and final release. In the same way that a captain who has made the Royal Guard surpasses a captain of the Gotei 13. We're probably seeing hints of Ichigo's next phase.