XCode has a nice feature in that you can easily create a 9-patch for an image in an image set right in the Asset Catalog editor. See: https://developer.apple.com/library/ios/recipes/xcode_help-image_catalog-1.0/chapters/SlicinganImage.html
It would be nice to have such a feature in XVS as well. It would also be cool to have in XS, but since this can be done in XCode, it seems more important to have this feature in VS to avoid a user having to move to another workstation to make a 9-patch from an Image Set.
Moving to Future Cycle.
Thanks for taking the time to report this issue. :)
Jimmy Garrido will be adding this to our VSTS backlog, as it is a feature request or enhancement.