I’m afraid there is no plan to bring Grammar Levels to the web at this stage, we are first focusing to perfect the features and the courses on the app before we branch out. Please bear with us on this one.
As for the Kanji, there is a guideline for when to use Kanji recommended by the government.
Public documents are supposed to follow this guideline (or even use less Kanji for non-native speakers) and many of the public sign posts follow this as well. In the new Memrise courses (released last November), I have tried to follow this guideline as much as possible.
The suggested guideline and the general trend now is to write it in Kanji only when it has that literal meaning. Some Kanji can mean both abstract and specific thing. For example, the word “時(とき)” literally means “time”. When we literally want to say “time”, as in for example “time will tell”, we write it in Kanji (「時が知らせてくれるでしょう」). However, in sentences like 「子どものときは、納豆(なっとう)が嫌い(きらい)でした」(“I didn’t like natto when I can a kid”), we write it in hiragana because it means “when” rather than the specific concept of “time”. Same with “事(こと)”, which could be translated to “thing” or “incident”;
- 考え事(かんがえごと)をしています。 I have something on my mind. I am thinking of some thing.
- 聞(き)いたことがあります。 I have heard of that before.
Another guideline of when to write in Kanji or not is; we don’t use Kanji when that is the suffix of the word, which is the case for 「私たち」. Here, 「たち」 is a suffix that adds the meaning of plurality. Where as in 「友達」, it is written in Kanji because it is not a suffix and you cannot separate the word 友達.
Above is the rough guideline, but people still write in a different way. Like you mentioned, there are people who want to use Kanji wherever possible to produce this “proper-ness”. I personally think it increases readability when Kanji is used differently according to the context.
Hope this helps! and thank you for reading this massive reply!