Some of this could be very good - I already get messages like "your next issue of 'Linux Journal' is ready" that tip me off to go grab it. It would be nice if this would auto-download and get synced up to my other devices - especially for things like bills, statements, etc.

But I tend to think that's a corner case (email based subscriptions notifications that need to be delivered by non-email means) - we already have tech to do this, between Microformats, RSS feeds with enclosures, and other established attachment formats like vCard and [v|i]Cal. I'm thinking that building on those rather than inventing new and arbitrary JSON syntax to enclose via MIME is probably a better long term strategy.

I also see the distinct possibility of abusive, antisocial behavior. Most people don't understand whitelisting, and the crazies among them already set their email clients to always tag every email from them as being "IMPORTANT", demand read receipts on everything, send HTML only messages, and worst of all, top post.