RSS/ Atom feeds already work great for sharing content. I’ve never stopped having an RSS reader and keep up with tonnes of blogs and comics that way. All my blogs have RSS feeds because syndication in this way is just easier, and reading things like comics/ big articles is better RSS fed than Tumblr fed IMHO. But the standards haven't evolved with how we're using the web these days. It's more interactive than firehose.
If the syndication standards were extended to add a “<3″ link, and a “reblog + reply” then we could replicate Tumblr’s reading-of-things-you-like functionality in a decentralised way. Searching wouldn’t be centralised unfortunately, but Google or whatever should still be able to find good content. You'd be able to interact; I'd suggest that reblogs are new post types on your own blog, with links to the source tree of how it got to you. Hearts are just added to a hearts counter on the original post, but they're registered on your site too so that it can show you posts you've hearted. I wonder if that’s worth proposing?