[hypest]

> you might as well just make a new protocol from scratch

This is the approach that so many new social nets are taking and then struggle to "convert" users. OTOH, "flipping some switches" to enable social features in someone's email client would probably be more straightforward for the majority of email users.

Besides, the "augmented email" would actually be a transitional model to "educate" the users into the distributed social net. After that, changing the underlining protocols to be a better/faster/cheaper ones would be natural for the techies and transparent to the average user.

> If you aren't subscribed to a source when it sends something out, you will never see that thing, even if you subscribe later

Well, from my POV, this is actually a benefit: I get the power to choose if the "new" friend gets to see all my history or not. As you later suggest, syncing wouldn't be a big problem anyway...