IIRC that's already something Facebook does with regard to the feed (as you mentioned). Say you get a friend request from someone you went to HS with, but outside of accepting the request you never interact with them on FB. They could post every day but you'd likely never see it.

I would imagine that the strength of the intersection of their graph with yours would play a role in this as well. Can anyone who works at FB comment on this? I'd imagine this is one of the back-end engineering problems the developers there would enjoy working on.