Board Thread:General Discussion/@comment-24749544-20140329111822/@comment-1268838-20140330173326

I don't think that it's particularly difficult to pull off (at it didn't seem to difficult when Renji did it once), but I think you are right on the money with the Bankai thing. Bankai is already the act of manifesting your Zanpakuto spirit, albeit in a subjugated form. Bringing it out in your ordinary form might not allow you to use it at all.