Recommend books that you can read with the kanji you know.

This is probably a moonshot, but imagine this: I am studying 200 kanji. I want to practice reading those kanji. Ringotan knows what kanji I am studying and maybe connects to a db somewhere that stores all the vocab for various books. It then recommends books that use kanji only up to the point I have studied kanji.

Conversely, we could select books we want to be able to read, and ringotan would make a custom review of all the kanji therein that we need to know.