ePub is basically just a limited HTML page in a zip file (plus a bunch of metadata and CSS styles), and ePub 3 can contain audio and video elements embedded in the text, just like a webpage. With the most basic usage, it would just show up as an audio player in the middle of the text, no sync. But there is also a media overlay thing I haven’t looked much into that looks like it provides sync.
Yeah, that makes sense. So it’s for the situations where you end up in an emergency shell.
Some better presentation of kernel panic would be nice (which I think is the closest equivalent to a Windows BSoD), but I guess it would require kernel support.