I'm less sceptical. FreedomBox won't guarantee privacy, but it might at least make it possible.
> structure that allows friends to see data that I've decided to share with friends
I think they'll implement a structure which allows each particular "friend" to see only what you want to show to that particular friend. For some people, you might show everything, for marketers and employers there'll be privacy features such as "Dud profile/password for employer" or "Dud 'friend' list for non-friend friends".
As for the wrench, it doesn't scale. Zuckerberg can give the data of a million Egyptians' Facebook accounts to a government for data-mining. Getting that same info via TCP/wrench is completely impractical.
For the problem of (real) friends reposting your pics on their Facebook page, yeh, that's a problem that will have to be solved. Still, from what I've seen of Facebook, people don't repost entire galleries from others. The limited flow of data between accounts will still greatly reduce how much data a government (or whoever) can easily get about you. Maybe that's enough already. In any case, FreedomBox seems our best hope, and the best starting point for a solution.