This is a pretty neat idea! I mostly get mistakes with kanji that looks pretty similar. This could maybe also extend to vocabulary. For example, I used to confuse theory 論理 and logic 理論. Showing mistakes in those cases would also be pretty helpful.
For now, you could maybe use two other methods that kind of do the job but aren’t as efficient.
The first one is the most precise, but will require you to either go to the kanji or radical page with which (resp.) the vocabulary or kanji is constructed, and will require you to kind of know what you’re looking for. It’s mostly about knowing what the other kanji kind of looked like (for example here both options have the temple radical), and then looking on the page of the similar radical.
Another option is to use the script below, which isn’t meant for this purpose, but also kind of helps with finding those pesky similar kanji. The advantage here is that it also shows up in your lessons and reviews, so you don’t have to go back every time. This is what it looks like on the item page, but it will also look like this during reviews and lessons:
