Both audiobook and podcasts listener populations have been growing dramatically. Popular audiobook players have supported MP4 Nero and QuickTime chapters for some time. Listen (Android audiobook app) now supports MP3 chapter metadata for the most popular formats and the other leading audiobook players seem poised to add support in the near future.
While MP3 tag provides limited support for Nero chapter data—I'm a little jealous of the attention playlists features receive—especially as they seem to be feature drift away from metadata.
Acknowledging that comprehensive chapter data support would be a grand effort, it is a true metadata issue that would be most appreciated. Even the ability to handle Nero/Quicktime chapter data in the manner that mpeg tags can be set for read/write/remove would be a boon.
Cheers and thanks for the world's best tag product and community!