Is There a Generic Theme Duplication Module or Drush Command As I understand there are Drush commands for Adaptive Theme, Omega, Zen and maybe other themes for creating subthemes, but is there a more generic module/way to create/duplicate a theme?  It would be nice to give clients a way to mirror their theme within the interface.
No but you can copy the theme folder and then replace the name of the theme in all hooks and of course rename yourtheme.info to yourcopy.info. in order not to miss any hook you may use a prog like wingrep and search-replace the yourtheme string