Functionality that would consolidate the duplicate files into a single file which is referenced everywhere the former 'duplicate' files were. - So all the files would still be available, but they would no longer be physical duplicates.
Suppose file 'A' is copied into five separate locations, creating a total of 6 duplicates. Converting 'A' to hard-links would place an NTFS link where the duplicate files reside. - transparently. Potentially freeing considerable disk space.
Each identical copy could be moved, deleted as desired. Only if a copy were editied, all would be edited. if a copy were deleted, only its instance would be removed, the others would be fine. I'm not sure I'm explaining this well, perhaps google lookup on ntfs hard-link might give a better explanation. There are products out there which provide this capability - TreeSize Professional is one.