The Japanese learning space feels so crowded. Most are marketed towards beginners, which makes sense when you see statistics (most folks give up). The top tier tools I recommend anyone are Wanikani and Bunpro. Beyond that, reading! I tried a site dedicated to it, but realized that I'm too much of a picky reader to do anything but read things I find interesting. So I read japanese and english books side by side now. I…
I really like their idea and feel such a platform would add a lot of benefit, since you can read whatever you care about. Sadly, the site struggles with longer texts (the UI is not optimized for it) and their flashcard system isn't that great. I have been toying with a similar idea myself. I'd love to read my ebooks with an easy way to look up vocabulary and easily creating flashcard decks containing all unknown words. However, getting the morphological analysis correct while providing fast dictionary lookup has been quite the challenge. This is the first larger project I've attempted so far, so lack of experience definitely is an issue in that regard.
So if anyone has some ideas, feel free to share them. It's not something I pursue commercially, so lack of market doesn't bother me.