Something really helpful would be a mode that gives you intervals that you guessed wrong. The more often you got it wrong, the more often you get tested on it. For example, I never get unisons wrong, so I have to set my own custom mode to remove unisons for focused training. But I keep confusing the semitone and minor 3rd, especially at the higher notes. It would be helpful to keep getting tested for those mistakes until my ratio of correct:incorrect improves.