Really, asking "what should replace Facebook" is putting things the wrong way around.
A more interesting way to ask the question is, "what did Facebook replace."
People used to build their own websites. People used to have blogs. People used USENET which was truly distributed and un-censorable.
Facebook and Google took the open internet and open standards and monetized and made everything crappy. Enough of that. Nothing should replace Facebook, it's done, stick a fork in it.
Facebook and google also just made things a few clicks and you have signed up, really easy. As @aral is trying to do with small-tech is make his tech as easy as facebook to sign up to.
Otherwise you put people off, what is needed is something to engage with, so unless there are celebrities on here for people to follow (and sadly abuse) we need to find ways to encourage engagement that they can't get elsewhere.
