I think Ichigo is getting a bit to arrogant on his Bankai. During the first attack he could definentley have done severe damage (or killed) Byakuga but instead he withdrew his blade. However, he let him go. Also... he didn't release his Bankai at the same time as Byakuga which is another point why I think either 1. he's going to be stupid and Zangetsu will have to spare him. 2. Some really bad crap is going to happen. Otherwise than that, was his first attack as soon as he stated bankai an amplified version of his Blade Cutting Heavens, the activation to Chain Cuts Heavens, or the performance of a technique under Chain Cutting Heavens? I doubt that his bankai is just him getting faster and stronger.