That's does make a lot of sense, it's just that my problem with Calibre is having to be at the computer to set it all up when I'd rather be able to just do it from my device as soon as I know there's an update via an email to my phone.
All that said, my brother did manage to bang something out relatively simple for those with small subscription lists!
Ao3updater.koplugin is here if anyone else would like to try and add any pull requests or whatnot. It's bare bones but what I was hoping for in making the Koreader device its own central station for adding and updating fic.