I'm working on exactly the kind of thing you're describing. Except ipv6 isn't really going to solve the connectivity problem as all the NATs and middleboxes on the network aren't going anywhere. We'll be using DNS instead as the 'identity' piece.
Since you said you would pay for such a thing, can you elaborate how much and what you'd expect (in terms of functionality)?
I would pay for storage videos/pictures/documents etc. This could be one monetization stone. My gut feeling maybe around $9.99 / month or $50 / year.
The basis everyone would except are normal social network features sharing of "items" galleries friend system feeds and groups.
Maybe this part should be an open source solution like for example diaspora.
On top of that you can build an app/service network. Maybe something like app.net.
Important on all parts is that you own the data and you should be able to pull it at will from any part of the network.
Since you said you would pay for such a thing, can you elaborate how much and what you'd expect (in terms of functionality)?