We do differentiate between DVD-Audio and DVD-Video.
The "CD" format started with only Audio CDs, but we also have releases in the database where a data CD is used as a medium to store mp3 files or similar. We should differentiate these.
So I would like a format
Digital Media -> Data CD CD -> Data CD.
(edit: This possibly conflicts with CD-R!)
In the same run including a format CD -> Enhanced CD might give additional information about the actual medium.
I want to note, that libdiscid ignores trailing data tracks and won't create disc IDs when no (CD) audio tracks are on the disc.
The relevant style is http://wiki.musicbrainz.org/Release/Format