That’s kind of what I was saying…not necessarily a bunch of completely different epubs, but simple “notes” files which could be imported to an epub. Obviously the epub would have to match the one that the notes were made with, but this wouldn’t be a problem since everyone could get the original epub from Mises.org, meaning we could ensure everyone would have the same source text.
Ideally, you could import more than one “notes” file at a time, and have all notes available at once. But I’m almost positive this is not possible. I doubt it’s even possible to export/import notes at all, but if it is, it’s probably through a process that is essentially creating a new epub file as you mentioned.
But yeah, what you describe is what I was talking about. Even though I have virtually no experience with e-readers (links for best ones are here), I’m pretty positive this is not possible (or at least, this functionality hasn’t been developed.) I doubt there’s enough of a demand for it…yet. I wouldn’t be surprised for it to make an appearance though, as e-books become more the norm. They’re already being implemented in colleges and university courses.
It won’t be long before professors are issuing importable notes to go along with the electronic version of the textbook…instead of handouts.