Why?
Common social networks are either dead (Google+ shutdown is right around the corner) or completely crap, insecure and horrible censored.
The idea is not new. Not even close. In some countries, such groups have more merit than any social network. So why not doing the same with the people around and their friends and so on.
No it's not public, but well, a censored public is not as important to me as an uncensored non-public space.