Earlier quoted context omitted.
How do you intend to tackle NAT, dynamic IP addresses, and devices that aren't always on, or devices only accessible to some machines but not others? How do you intend to solve the chicken and the egg problem this network will encounter?
IPv6 is already being deployed from top tier mobile carriers and that allows globally rout-able addresses even behind NATs. If you have no social graph on yada, then your very first connection to a friend may have to be unencrypted, but not in every case.
You're making a lot of assumptions:
1) That IPv6 will assign a unique and constant IP to every device. Many ISPs provide this as an up-sell feature, not the default, and I don't expect them to change their behavior even if the cost of it approaches 0.
2) That IPv6 will solve all your network problems. It doesn't solve the issue of a bad link or a restrictive firewall. Consider Hosts [A,B,C] and Firewall F. F will block all connections from B. How will yada connect A and B in this arrangement: A [B,C] ? Will is use C to route the connection? How will it determine that C can act as an intermediary, and how will it protect A's data such that C can not be used as a MTM (Man in The Middle) attack vector?