Is there a script to turn kanji and katakana into romaji automagically? I use beets to organize my library and I presume you can extend it through a plugin to add the sort artist tag automatically, which is not a bad idea at all.

Kana should be fine and there seem to be plenty of scripts for that online (you could even probably copy/paste the table from wikipedia into a python script and add some commas to make your own), but I couldn't quickly find any for kanji so you'd have to call out to google translate or something and give a confirmation prompt for each translation, because they will all be wrong. Maybe there's a kanji->kana script designed for learners that you can use in 2-step translation