For the love of all that is holy, please do not do this. Or if you do, at least make it admin and user configurable.
The whole damn internet is turning into disconnected bubbles of information as 'intelligent' software makes decisions for people about what it thinks they want to see, as evidenced by the Facebook/US election coverage debacle. It's a terrible, terrible direction I hope you don't get suckered into following for the sake of mimicing other software trends.
If your modern forum software is truly designed to encourage conversation, that goal won't be served by deciding for participants what they may be interested in. The software already has user available tools for that (mute), so leave it at that.