The ability to add audio and video clips to posts would be a welcome addition. Video can already be added by embedding a YouTube or Vimeo video, but this comes with some restrictions such as being bound by the external provider’s terms of service. It also creates a dependency on centralised social media platforms.
There is a lengthy discussion about adding audio and video support to CommonMark using the existing image syntax with the usual audio and video file extensions, e.g.
I think Ghost would be an ideal platform to implement this extension on; using the same drag and drop system used to embed images an author could embed an audio or video clip in their post.