Highlights, bookmarks and show notes
A show notes system for avid listeners could be made. Listeners could add their own private notes to any episode or audiobook. They could opt to make their show notes public, providing their commentary and summaries for others. This could be like Evernote and/or Genius for spoken-word audio.
How it would work
This would function very similarly to the Universal Comments system.
Basically, there would be central server where the notes and user profiles would live. Timeline-enabled apps could integrate the show notes platform via the platform's API.
There also could be direct integration with Evernote.