Perhaps mk could set up a system where some number of comments will pull a post off of Unshared without it actually being shared?
I like that idea. It's simple. I should also add that there is a 'globally ignored' function, syncretic. There are only a few accounts that have qualified, mostly selling French hotel rooms, but if a user gets lots of ignores with few positive signals, they can still post, be shared, and followed, but they don't appear in these streams. I am planning to add a 'see-globally-ignored' toggle in the controls page, where users have the ability to include what everyone else doesn't want to. Maybe you need a French hotel room. It will default to off, of course.
That sounds reasonable - the entire point of the "unshared" tab is to find new content from new users (stuff that might not have gotten shared if you hadn't been looking for it). If several people have commented in a thread, but no one has shared it, that's probably a good sign that the post is not worth discovering in the first place.