His Bankai his most likely his full Hollow transformation. Why? Because his Hollow powers are the roots to his Zanpakuto powers. Also, H2 Ichigo is a transformation which makes no sense thus far, and that very form was able to do some Jedi-shit with his fake Bankai. So connect the dots: Ichigo's true Zanpakuto comes from the powers of his Hollow + a mysterious Hollow form what uses his fake Bankai to the fullest extent = real Bankai is 100% Hollificication.
Furthermore, he may be able to use the Quincy: Vollstandig in conjunction with his Bankai.