Hey there!
I' ve found your OPDS-Content-Server or whatever it sshould be called
and it is really great.
Theres no more need of calibre2opds for me and it is running great on my little NAS.
I've added some code for displaying Books by Genre in a seperate Category.
This is done by creating a custom column in calibre and telling your application how it is named (by looking into the metadata.db-file, for example "custom_column_6".
Let me know if you are interested in (integrating) this code.
Cheers