I gave Bakuto's bankai some thought.  So far I have thought of a bit of a mixture between Ichigo's bankai which is shrinking down the overwhelming size of a bankai to increase speed and power.  The other is a bit from the Bount filler using the idea of how the bount's leader could use wind attacks, turning Bakuto into his own Bankai.  Creating swords of wind from his arms, enveloping Bakuto's strikes punches and kicks with intense wind enhanced speed attacks. Speed faster the normal Shunpo/Flash step ect.