Videos, audio and photos and game media will take the bulk of the space. Of those - only photos and a proportion of the videos are likely to be totally unique to a user.
Consider that Dropbox gives you 50gb for the basic plan. I'm guessing most people don't back up videos, games or their OS using that space, but rather back up their documents, projects they're working on in whatever field, photos, and music.
Of those, only with music is there a chance to use deduplication, and that's assuming you can figure out two music files with different ID-tags are the same.
(Come to think of it, in my Dropbox, music easily takes up 70% of my quota, so maybe is is worthwhile after all.)
You need a decent hash of every file anyway (to check for changes etc) so it's pretty trivial to deduplicate. I don't think you'd need to do stuff like check the ID-tag.
Consider that Dropbox gives you 50gb for the basic plan. I'm guessing most people don't back up videos, games or their OS using that space, but rather back up their documents, projects they're working on in whatever field, photos, and music.
Of those, only with music is there a chance to use deduplication, and that's assuming you can figure out two music files with different ID-tags are the same.
(Come to think of it, in my Dropbox, music easily takes up 70% of my quota, so maybe is is worthwhile after all.)