I think a really helpful feature would be to automatically vary the question format. Right now, question type can only be changed at the deck level, and it can only be changed at the start of a review. But we all know it can be helpful to learn from multiple angles - you read the word in Japanese, you see it in English, you hear it only (this should really be added).
To address this, I suggest the system be able to randomly select different question types. Or just pick a different question type vs what was seen last for a given card. Could do a few variations like that. Would definitely help with memory retention, hopefully not too hard to implement.
Cheers!