Ensure the player is playing the note for the right length
It is very important for a player to the get the length right and yet, it's a major drawback of Yousician, which only checks is the note is pressed at the right time. However, if the player plays a 4 beat note for 1 beat Yousician is happy - this is wrong.
I understand this is complicated to do with out MIDI but with MIDI it's certainly possible and should be enforced. It might put people with MIDI in challenges at a disadvantage but we are here ultimately to learn the piano, not to win challenges.
Graham Clark commented
Totally want this! At the moment I record my performances to my workstation and look at recorded score too check my note accuracy.
I imagine many people are holding notes during rests and or incorrect lengths.