Doc Searls writes about what it would take to build it:
First, I think we need protocols. These should be modeled on the social ones we find in free and open marketplaces. They should work like the ones Sayo talked about in his Socratic dialogue with me on the airplane. They should be simple, useful and secure.
Second, we need ways of supporting transactions. This is a tough one, because to work they need to be low-friction. I should be able to pay IT Conversations (or any public radio station, or any podcaster) as easily as I pay for a coffee. Or better yet, as easily as I tip a barista. So PayPal won’t cut it. (Not the way I’ve experienced PayPal, anyway.)
Third, we need ways of selectively and securely asserting our identities, including our choice to remain anonymous. This means getting past sign-on hurdles on the Web, and past membership silos out in the physical world (such as the ones that require a special card, or whatever). Again, the friction should be as low as possible.