These were my thoughts when I wrote it:
1. Most stuff being shared is of no value to most people. Does not encourage exchange of good ideas. Sharing, as it works now looks like a fad. It has peaked. Most people I know are bored now, it's just the inertia that keeps them there.
2. If someone is genuinely interested in something, they will seek out good communities to join. HN is a good example. And Slashdot (much more so earlier, but even now), gamer forums, some reddits, astronomy forums, photography etc.
3. There would probably need to be a tool to share with family and close friends. But that doesn't need to look like FB. Then again, Social networks help fight against totalitarian regimes. FB would be missed here, although I think Twitter plays a bigger role.
Josh Miller in "The Next Facebook" makes an interesting point: The next network could be about making it easy to talk to people you don't know so well. Example, again Hacker News. https://medium.com/musings-about-text-boxes/8157c364d26a
I am working on some related ideas, for open communities and forums. This will be open source, and I'll document, share and collaborate on the entire process of designing this application (like discussions, whiteboards, sketches etc) . Plan to start this week, if interested add me on Twitter (@jeswin). Code isn't committed yet, but it will be here: https://github.com/jeswin/fora
PS: This was written in a hurry. I apologize for mistakes. I have to leave now; I'll check comments later in the day.