Doesn't work for torrents with RAR/ZIP files. The ref-link is also one-way. If I have existing content on my disk, and want to (partially) seed a torrent - can't do that easily.
I'd like a way to say: "Everything inside /public is public-domain content, seed it against any valid torrent if someone shows up with a valid hash"
on my laptop with btrfs this requires no special effort: simply copying the files and renaming them suffices. nautilus (gnome file manager) uses copy on write, and coreutils "cp" also defaults to "reflink" these days.