I started coding again, and am currently brainstorming the implementation of the "demote flashcard" feature I described earlier. Essentially the ability to reduce the review interval of a card, when you forget it, instead of sending it straight to the restudy pile. With this change I will also add the option in the flashcard dropdown, to force a card to be sent to the restudy pile, so in the end you have a more fine grained way of managing the restudy pile.

While mulling over this I realized that this isn't as straightforward as I thought with the Leitner system. So I am considering converting the Leitner SRS to something closer to that of SuperMemo, Anki, etc. Instead of storing the "box" each card resides in, it will store the review interval of that card. Along with that a "mutliplier" setting, which can be added to the user's preferences, is used to calculate the increased intervals. So for example with a multiplier of 2, the intervals would be 3 days, 6 days, 12, 24, 48, etc. Once the SRS is updated that way, the "No" answer can be configured to reduce the review interval instead of sending the card straight to the restudy pile.

So the way the "No" answer would work is to first reschedule a failed card within 1-3 days (probably a user setting), and at the same time recalculate its interval as a fraction of what it was before. So if the last interval was 30 days, and the card was forgotten, it could be 10 days. Now after 1-3 days the user reviews this card. If the review is then successful, the card will be scheduled again as usual, but its interval has been reduced. So this would be roughly similar to a card moving down several boxes, however the way the Leitner data is currently stored doesn't work which is why I am mulling over this change to the SRS.

ps: another thing that came to mind is that I could potentially add a new "Relearn" answer, so the answers would be "Relearn", "No", "Yes", "Easy". So if you don't like the restudy cycle, you can just answer "No" to demote the cards and keep on reviewing (keeping in mind Koohii SRS lets you view and edit the story while reviewing). If you answer "Relearn" then the cards will be separated into the red pile which can be worked on in the Study section.