Finally… the time has come… I managed to implement a simple table, yay!
Here is my personal (at the moment rather short) info table for the interval of a month:
As you can see the time frame can be set in number of days and months. Then a table with reviews, accuracy, and lessons - divided into radical, kanji, and vocab - is displayed. You can look at the development of those criteria in the intervals you specified (and can go back as far as you want with the arrows at the top). The current day is never counted.
I hope you like it!
Also, this is currently not the WK stats accuracy, but the one at the end of reviews. I’ll implement the other one in the future if you like it more.
Done that! It looks way better. I tried to imitate the wanikani-community-style of blurring the furigana until you hover over it. I hope it isn’t patented 
Added it, great suggestion!
I also added a “Started” and “Finished” info to each level which I thought would be interesting to know in absolute time:
And now finally, @UInt2048 I would really like to work together with you to implement your projections userscript for wk stats in, for example, the level chart. I.e. I would like to let people see visually how long they are going to take to finish; like a level chart that automatically has a projection up to level 60 and maybe a slider where you can set “fastest”, “median”, “average”, or “off”. If that is what you had in mind?
I don’t know if Sully22 wanted to create something similar? It would probably be pointless to create the same thing twice. But from what I have read he wanted to implement it as a table. Then we would have two different ways to view the data which is good in my opinion.
I also really like how Nihongo Stats looks and works. It is a really great idea to have data from multiple Japanese learning services combined into one overview. Now I’m kind of depressed haha 