It would be great if the Report Suite Segments in SiteCatalyst 15 were available in Discover too. It's especially annoying because if I were to re-create the segment in Discover, it will show up twice in the SiteCatalyst segmenting menu.
This is now available with the Adobe Analytics Spring 2014 release! We have made it so that a segment created in SiteCatalyst (reports & analytics) is automatically available in ad hoc analysis, and vice versa.