I think that, as other people have pointed out, people might not be looking at the explanations once they reach the higher levels. More importantly, however, is that implementing such a feature successfully would probably require a change in users’ mindsets: I believe that most people on WK use it to learn kanji and study a bit of vocabulary. By default, what most people desire in such a situation is something that explains things as clearly as possible, in a manner that’s accessible to them. That means that explanations in English are the natural choice, seeing as WK’s target audience is English speakers learning Japanese. Doing things this way means that the effort required of users is minimised, allowing them to absorb the material easily and focus on learning new words and kanji. Your suggestion, on the other hand, would require users to treat WK as part of an immersion experience in order for the added Japanese text to be useful. It might also make some users feel that WK is unnecessarily cluttered. Another thing: some mnemonics or explanations might rely on Anglo-American cultural references, which could make them very hard to translate.
I’m not saying that your idea is a bad one by any means. I would probably want it if I were actively using the WK SRS. I’m just saying that I’m not sure how many people would want to use such a feature, particularly since
- There is no guarantee that a WK user has grammatical knowledge to match his or her kanji knowledge.
- At a given level, it maybe be difficult to construct sentences that are composed almost entirely of words WK that has been covered before.
As things are, there are already example sentences on WK, which certain people may already be using for reinforced learning and studying grammar.
Please don’t take my comments to heart. I don’t intend to shoot your idea down. It’s just that I’m not sure how viable it would be, even if it’s great in theory. It might be better to look for native material (e.g. anime, newspapers, manga, websites…) for the purpose of immersion, and to take advantage of the Japanese practice threads on the forums. (N.B.: Grammar in posts isn’t perfect even in the advanced Japanese section, so don’t forget to check how the structures you see should be used. It can be good practice otherwise.) Also, I’d suggest using a good dictionary, like ejje.weblio.jp or Jisho. (Honestly, use both, because as great as Jisho is, I don’t think it has everything, and the definitions aren’t written by native speakers anyway.)