Until this is implemented as a feature, the work-around I have been using is to manually define text anchors for the notes-in-text, then hyperlink them back from the end-note page.
I've discovered that when I do define text anchors and hyperlinks in this way in an indesign document, the Epub export fails. When I say it fails, what I mean is that Indesign freezes during export and has to be shut down manually via Task Manager (in Windows 10).
I'm wondering if this might be due to the manually created hyperlink conflicting with the automatically generated hyperlink from the epub export process.
However, I would expect an error message or warning of some sort rather than a complete crash of the program.
It would be intersting to know if anyone else has encountered this problem or can offer a solution?
It's not a huge issue since I can always leave out the hyperlinks until I need to specifically create a back-linked pdf, then create a copy of the original indesign document for the specific purpose of exporting a pdf version. Still, it seems a cumbersome way of going about things!