https://media.blackhat.com/us-13/US-13-Davis-Deriving-Intelligence-From-USB-Stack-Interactions-Slides.pdf
Page 27 of this research from NCCGroup may be of interest in doing OS detection. There are apparently some slight differences in how the USB enumeration process happens between the various OS's.
I'm not sure if the Bash Bunny can view the USB protocol at such a low level, but if it can, this approach would certainly be optimal. Opening up another powershell/python or whatnot just to do OS detection increases the time required to exploit, and potentially increases the chances of being caught.
