One issue I can see is that you only need to have one friend who uses a third party tentd with questionable privacy policies and now everyone they're connected

One issue I can see is that you only need to have one friend who uses a third party tentd with questionable privacy policies and now everyone they're connected to has their data exposed. Would it be possible to implement it such that you can say 'yes, you can have this data, but only if your server is not being run by 'blacklist' (would have to assume the requesting sever doesn't lie about it's identity). On the positive I can see this catching on because it's easy for existing social networks to integrate, it would almost become do or die forever more if a network that does integrate them catches on