@Philosopher, are you still looking for an AudioBook plugin?
The idea sounded interesting to me, and so I threw together a Metadata Reader for AudioBooks in the .MP3 format. Very limited for .M4B format.
@Kovid, It is up at https://www.mobileread.com/forums/sho....php?p=1667632
It is still version 0.5.0, so has a ways to go.
1: multiple files are still separate "books", but are put in the same series together.
2: still having issues getting the cover image out of the .MP3 file (if present at all).
3: still having issues setting the mi.pubdate and mi.title_sort.
4: no way (yet) to send a books playlist of all chapters to an audio player. ;-)
If you "open" a single book and it will probably play in your OS's normal way.
5: does not write modified metadata back to the MP3 file. it is a Reader plugin.
PS: The default book cover, if I can't find anything else, is a small PNG. I tried to use an SVG, but it didn't display properly. It looks like total or partial transparency is failing on both SVG and PNG. (in calibre 0.8.10 on Windows-7). Both files are in the zip.