So long as we remain wedded to directory paths as a means of referencing files and folders, much of our storage will contain duplicated content.
As a counterpoint, there are many situations where duplicating content may be preferred. If I'm pasting something into a document, I want it to remain immutable there without the risk of an external change (by me) altering the document that I assume to remain static.
I would add that in general there is no one right abstraction. If you want to be able to change the source file, you are best of using symlinks. If you want to be able to change both files and keep them in sync, you should use a hardlink. If you want to create a true copy and modify them independently, just make a copy.
Also worth mentioning that most COW file systems support block level deduplication, so if enabled, two files with the same content will be stored only once.
Rather than semantically splitting the original content (by either using unidirectional links or getting rid of the connection entirely), it seems to me that keeping the content in a versioned database with bidirectional links is much preferable from the user's point of view.
The versioned database takes care of grouping related edits and lets you point at a specific, immutable version. While bidirectional links let you efficiently find all usage sites so that you can make an informed decision as to whether they need updating.
As a counterpoint, there are many situations where duplicating content may be preferred. If I'm pasting something into a document, I want it to remain immutable there without the risk of an external change (by me) altering the document that I assume to remain static.