I cannot overstate how much I’d like to thank @rfindley and @BIsTheAnswer for their help in getting this shipped out ASAP 
New version of this user script is live! I’ve updated both the OP and the GitHub page with details on the new changes, features, and installation requirements.
The REALLY big deal right now is that this update fixes the script to work as it used to before the recent compatibility mode changes that were released – version 1.0.0 of this script will literally just not work at all going forward. Install the latest version to get back to your usual routine! 
2 other major things to note right now about this release:
- it was blitzed over the course of these last days, so if there’s some QA issue like a typo or broken link: that’s the reason why
as usual, please let me know if anything comes up
- thanks to the WaniKani Open Framework dependency that was added, I was able to create a whole new settings panel that exposes some config options that were previously only accessible by editing the user script. Not only is the new panel integrated into the UI, but it’s been set up to persist configuration across future upgrades and installations of this script – I highly recommend you check the new panel and play around with the toggles there!
Again, sorry for the delay in releasing this fix, I’ll be better about keeping up with WK developer announcements going forward! 
Edit:
I totally forgot to mention this, but I’ve updated the install instructions in the OP. To update, just reinstall if your userscript engine doesn’t update the script version for you 