I made kepubify based on the KoboTouchExtended driver, my findings in the firmware, and a few existing kepub books. After I implemented the basics, I added a few unobtrusive features (like CSS addition and text replacement), and made seriesmeta.
About a Calibre plugin, I kind of
got started on making one, but I never finished it, as I didn't really see the point (I don't use Calibre, and the Calibre conversion process mostly negates some of the benefits of using kepubify).
I suggest you decide whether or not you want to use Calibre, and go from there. Note that you can import books converted by kepubify into Calibre if you have many books, and you want the speed benefits of kepubify, but still use Calibre for management. If you are just transferring books, you might as well just use kepubify and seriesmeta by itself, as that is how it was meant to be used.
I use the following script (on Linux) to sync my books (I've simplified it a bit): git -C "$HOME/Documents/Books/Books/" pull && kepubify --update --output "$(kobo-find -wf)/kepubify" "$HOME/Documents/Books/Books/" && umount "$(kobo-find -wf)" ; seriesmeta "$(kobo-find -wf)"
P.S. My homepage is quite outdated, and I'm working on a new one when I have time. You'll find my latest projects on
GitHub.