Would you be open to integrate the ID3 chapter frames: http://id3.org/id3v2-chapters-1.0 This makes it possible to use chapter marks in all mp3 files!
In the german podcasting scene this format is already used by many people and displayed by podcatchers on Androind (the open-source AntennaPod, https://github.com/danieloeh/AntennaPod) and iOS (e.g. the popular instacast http://vemedio.com/products/instacast).
It really makes sense for podcasts, audiobooks etc. - most of the time you have to provide an MP3 format (because all old cheap players support it) and with the ID3 chapter extension it's possible to add chapters too, which is especially useful for long podcasts.
We (http://auphonic.com) already implemented this for the eyeD3 0.6.x version, but I have seen that you did quite some refactoring, so maybe it's not so easy to merge ...
What do you think, would you be interested to include this in eyeD3? I would be happy to send you our modifications to eyeD3 and maybe we manage it to merge it into the latest source.
Thanks and have a nice day! LG Georg