I've seen this on other apps, and it really helps. Every word you didn't know in the crossword could be added to a Japanese vocabulary list on the app. This could help when people are trying to expand their vocabulary or attempt the more advanced puzzles, and didn't know the words before. And since Renshuu also does vocabulary learning, it'd be nice if the Renshuu app and the crossword app was LINKED.
For example, if I looked up the new word I didn't know, and had a button to add it to a learning list for the Renshuu app, then I could go back and study it. Is there a way to do a collective vocabulary list for the J-crossword app?
*Note this is just an add-on idea I thought would be nice to have*