User blog comment:Xilinoc/Ch. 541 - THE BLADE AND ME 2/@comment-10797017-20130614060634/@comment-3230060-20130617140656

Nah, just like you never saw Unohana's bankai, you'll never see zaraki's. The kenpachi bankai, as i believe, is to pass on the asuchi to the next kenpachi. Which keeps increasing it's power level after each of the pass downs.