don't deduplicate files in the file system, just across snapshots
are handled at the file-system level (meaning you'd have to create a separate file system, or at least a separate subvolume if you're already using btrfs, to make them with an exclusive set of files)
don't have access controls beyond Linux' basic file controls (so sharing a server will be complicated)
aren't served across the network (you can serve a btrfs file system, but then you can't access a previous snapshot)
aren't portable (you can't just copy a set of files to a new server, you have to image the partition)
They serve a very different purpose than a deduplicating file server. Now, there are other deduplicating file servers, but I don't know of any that are open source and run on Linux.