Since the iTunes playlist support is kinda weird and breaks if you have smart playlists, I've been looking for a way to sync my iTunes playlist into Plex. I finally gave up and wrote something myself, using Node.js.
It's pretty basic at this point, you give it your
iTunes Library.xml file and Plex server info and it will make eleventy-billion queries to match up Plex songs with their iTunes equivalents and put them in playlists named after your iTunes playlists.
Things it doesn't do yet that I want it to do:
* remove songs that have been removed from iTunes (ie, proper sync)
* reorder songs to match the iTunes playlist (if you have moved things around)
* delete a playlist if it's been deleted in iTunes
* keep state and only do queries that are necessary (ie, I'd like to store some metadata about iTunes song IDs in Plex tags so I can avoid messing with already-updated stuff)