We can export easily to ePUB, too, but the e-paper native app will be cooler because then you don't lose all of the Nostr features.
But we have to start someplace and ePUB is easy because Asciidoctor already comes with that. ePUB, LaTeX, and Asciimath.
I think people wonder why we're going through all of this trouble, instead of just adding zaps to a PDF viewer, but... it's already got some awesome capabilities and we haven't even finished v0.1.0, yet.