Pandoc can already convert from epub to markdown and we have a markdown to 30040/30041 converter/uploader that we're already using to publish books. You can already convert all the books. Would be nice to have a pretty online website for doing it, I agree, but that's not really what we're discussing.

We're discussing a nostr-Native e-reading app that imports and exports ePubs (or any other format, pandoc does all of the major ones), but uses notes stored on relays internally.