Kavita has a custom epub library that actually streams the epub pages. The reason why it's non-existent is due to epub being a zip, with a manifest of pages and images. Each page is an html document, so it may have images requested from that manifest.

Most applications just use epub.js which needs the whole book loaded at once.

Edit: Also Kavita does support some calibre tags for metadata and def is much more customizable with a powerful filtering system which you can then bind to your dashboard/side nav.

www.kavitareader.com for those that might be interested (or check the wiki to get a bit more about it).