Currently, the "work around" for supporting an audio-only course is to convert the audio to mp4 and use that file. You can add an image for this so it displays while the audio is playing, however it doesn't work on mobile. As soon as the audio starts, the screen goes to black. This request is to keep the image on the screen for the mobile experience.
+1. Podcasts and audio learning are getting more popular. Our users need better visual feedback that a module is audio-only without us needing to convert these files to mp4s. Absorb should make this easier for us either by adding an audio player, or like you mentioned, allowing a thumbnail to be uploaded and persist through the playback.