Human communication and meaning-making needs to happen on a smaller level. A few hundred people with common values and ideas. People who share something with each other. The social internet is a great place to explore a common niche interest, but pretty much toxic sludge for anything else.
Somehow make it hard to hide the fact that you're a bit.
Get rid of connection oriented protocols like TCP.
I've always wanted to at least see a social network where everyone's identity was verified. Seems like that would eliminate a lot of the things people complain about. (Spam, harassment, misinformation.)
I've also wondered if there's a way to make it 100% non-commercial. (Maybe with government funding?) Public television was created with the idea that if this medium was going to exist, there should be one channel devoted to the greater public good (and not commercial pursuits). What would a social network be like if it didn't have to make a profit because it was publicly funded?
I've always wanted to see micro-social networks. (Imagine a Facebook or a Twitter, just for your town/university/book club/whatever.) Maybe public libraries could be involved in creating them, or local newspapers, or school journalism classes...