Listening-based social network
Timeline allows for comments to be attached to words, chapters or any other annotation.
There could be a universal commenting system that plugs into any Timeline-ready player. If a listener makes a comment within one app, it displays on all participating apps.
This could be expanded into a full-blown social network for podcast and audiobook listening, discovery and discussion.
Universal comments for podcasts
There would need to be a central server and database where comments and user profiles exist. Comments would be stored, along with the locations they refer to on the Timeline for the given episode.
Comments or comment threads attach to the timeline just like any annotation.
When you open an episode on a player apps that supports Universal Comments, it would display the comments, attaching each to the episode timeline. All podcast shows have a unique RSS URL and all episodes have a GUID that is unique within that show.
That information would be sent to the Universal Comments server and the server would respond with all the comments for the episode. The player would link those comments to their designated spots on the timeline.