This article gives me a little more insight.

Listening to the video, it seems LinkedIn is already trying to do this. It often lists the degree of separation from the user and people posting on the feed.

One flaw I am seeing is that many users of social networks are rather flippant as to who they let into their group. I believe LinkedIn used to message that we shouldn't let in strangers to our primary network, but I haven't seen that messaging lately.

In my case, I would not consider any of my 80 LI contacts as my Dunbar group. Maybe 10 would be secondary. The rest are strangers or almost strangers.

I'll have to think more about this.