Audiences for federated social network technologies

I've been very happy to see the great discussion going on here.

One question that's come up is: who cares about federation? I think 
there are a lot of parties who benefit from federation. For example:

  * Privacy advocates - can engage with social software without handing
    over PII to ad-driven networks
  * Free software enthusiasts - can use Free and Open Source software to
    connect with friends and family.
  * Open Web enthusiasts - people who are concerned about walled gardens
    and captive networks can participate on the Web instead.

I think there are some other audiences, though, that could be extremely 
valuable.

  * Commercial social software developers - software developers either
    have to pay a high fee (30%) to participate on some platform
    (Facebook), or might have their access denied altogether for certain
    kinds of apps (Twitter). A platform that's competitive could allow
    access to a whole new range of developers.
  * Advertisers - Advertisement is banned on Twitter, tightly managed on
    Facebook. Finding ways to use federated social networks for
    advertising could be huge.
  * Families with children under 13 - The COPPA act has high
    requirements for services to collect private information on children
    under 13. Most social networks don't bother and just ban kids under
    13. With children well under 5 able to do basic tasks with tablets
    and phones, I think there's a huge untapped market here. And if Mom
    set up the network on her own server, she's (probably - IANAL) not
    subject to the same COPPA rules as a commercial service. And except
    for families that practice exclusive endogamy, family networks are
    naturally federated. (Thanks, sexual reproduction!)

For some of these audiences, a big base of users (1M? 10M?) is required 
to get their attention. For others, like families, the most important 
network effect is in your own home, or with Grandma and Grandpa.

-Evan