Hi Chris, in some ways, the Reader feature of WordPress.com implements some of this. The user can subscribe to websites, read the content, like the content, and respond via comments; all within the Reader.

I think with a bit of tweaking (and desire), Automattic could add the ability to make those comments available as new posts on the commenter’s website. It would make WordPress.com (and JetPack supported self-hosted WordPress) more like micro.blog.