One of the issues that many kanji learners have is that there are a lot of kanji that are similar to each other (氷 vs. 水). Learning these kanji in isolationi is sometimes frustrating since if I need to learn how to dinstinguish them I need to understand in what ways they're different. Since Renshuu can easily know what are the pairs of kanji that people often confuse, it would be nice to have a study vectors where keywords are presented (e.g., `bundle, sheaf, ream, tie in bundles, govern, manage, control`) and the user needs to choose between two similar kanji (束 vs. 東).
While I do agree that is an area that could be improved, I do not think that adding a new vector would be the way to do it. That vector would be more of a quiz type less so than a vector, and doesn't really "fit" in with the rest of them.
Now, a number of the kanji quiz types will attempt to choose visually similar kanji when doing multiple choice (say, definition > kanji). A more effective approach in the future may be a way to suggest to renshuu that you want to focus on visually similar ones, compared to ones that have shared readings, for example.
