To be honest, the closest thing to an interest feed as you describe it is tumblr — not because it doesn’t try to be a ‘social network’ but because it fails so hard at being a bidirectional communication medium.
Like twitter, tumblr has asymmetric following and a reblogging feature that constitutes most of the content. Unlike twitter, most active users keep separate accounts for separate topics. While you are still *following* *accounts*, it’s more like following one person or group’s curation of a topic than it is like following a person, and some portion of the network actually only pays attention to tags (meaning that they don’t follow anyone and don’t look at their feed, but instead watch a topic-centered feed via the search function). So it’s twitter without character limits.