[Quoth]

I'm underwhelmed.

I create and manage content with wordprocessor files and image files and the directory structure.

I manage metadata etc with a spreadsheet, KATE sessions of pure text files and Calibre.

Amazon is only one of many Retailers. My spreadsheet has the first date, last update, publish ID etc of each Retailer that has an Upload destination for each format. It also has current status of every work, last update date, word count, series, tags, genres, cover source and what checks have been done.
I really should use a custom database, but currently the spreadsheet is fine.
Everything is backed up on different things.
The actual files have version numbers in the filename and actually in the Frontmatter.

I simply upload files from the suitable directories for content and cover, and copy paste all the Retailer Meta data from either the Spreadsheet or a section of the Master Blurb file.
Also there is paper and audio as well as ebooks.