Idea: Plain-text files for storing ebook progress and notes

[ParotidApps]

What do you think about the idea of having a standard plain-text format for storing progress and notes for ebooks or even audiobooks?

I'm thinking two separate files: a .progress file and a .notes files, eg
MyBook.epub.progress and MyBook.epub.notes.

They could both be plain-text TSV files, with a # commented header line with any additional info. TSV has the advantage of being very easy to edit in any text editor without having to worry about escaping commas.

The progress file could keep a list of timestamp and position every time a book is opened or closed, with the last line being current position.

The notes file would keep all highlights and bookmarks.

Would it be annoying to have two additional files being created for every ebook? Maybe a single file would be better, like a MBP file but plain-text (JSON or TSV)?