Board Thread:General Discussion/@comment-27140233-20151102183905/@comment-26091912-20151103061206

^ I think what he's trying to convey is that when a Shinigami has fully mastered their Bankai, they take on an appearance resembling their Zanpakuto spirit. And their Bankai also becomes more physically fused with their body.

Renji is also the first one to reveal his Bankai after training in the Royal Realm. So it is possible that Byakuya and Ichigo could have a "new" one, as well.

Besides, it's not like Ichigo's Bankai hasn't changed appearance before.