At the heart of any ranking aggregator, however, is the ranking. Currently, there is no ranking within the PM system, therefore putting it somewhat aside and parallel to core aggregator functionality.
By adding ranking to PMs, they become directly competitive with the core functionality - the same, in fact, only with added echo-chambery goodness.
And that's my real problem: Hubski is already a bit of an echo chamber just because the size and community tends to attract like. Most of us are pretty good folx. A "shadow Hubski" could be the absolute opposite of that, and considering hubski's sterling moral character, I suspect very little snooping would happen. But we can't even really test that because there aren't enough nasty shits about to truly see what a wretched den of scum and villainy could be created.
Can anyone add anyone else to a PM conversation? Can anyone remove anyone else? How does blocking/muting/hushing work within a PM? My concern is not that this is a good or a bad thing, my concern is that this is a complex thing with difficult-to-map consequences and that none of us will really have a handle on what it does until it has irrevocably shaped Hubski.