OK folks! You spake, and I listened! Introducing the Wanikani accuracy and review pacing webtool, at this address: Wanikani Statistics ! What a mouthful.
Basically, just feed in your v2 API key, and it will use your past reviews to compute your accuracy per level (including various levels drops depending on level and number of wrong answers). Then you just need to provide your lesson rate, and it will do All The Math ™.
Enjoy!
(If anyone has CSS skills, please feel free to make this pretty, I’ll happily apply your changes…)