Board Thread:Questions and Answers/@comment-28648393-20160728233147/@comment-29359011-20160729191155

Look closely to his Bankai peoples: http://otakukart.com/animeblog/wp-content/uploads/2016/06/006.png

You can clearly see the outer white blade cover a inner black blade. I think the white blade of his complete Bankai represent his hollow powers and the black blade inside it represent his Quincy powers. When his outer white blade was shattered by Yhwach it only exposed the inner black blade inside it who end up looking exactly like his first shikai form. So its not really a reverting back to his old form thing.