This feature would be extremely beneficial to me. I find it frustrating while in practice mode that I can't scroll through the song after I played it to see where my timing was early and late.
I've been using a different (free!) app as a chord trainer, which necessitates me adding all the chords I've learned in Yousician into it. I generally start each day's guitar practice by reviewing all my learned chords randomly for 10 to 15 minutes before diving into a new Yousician lesson. I would love for this feature to be added to Yousician.
This is my number one request. When I'm having timing issues, I try to focus on the bouncing ball to hit the note correctly, which makes it difficult to see and comprehend the feedback on previous notes (e.g., "Early", "Late", "Perfect"). I would prefer if the feedback persisted, and then to have the ability to simply scroll back through the song to see where I'm making mistakes. The inability to review performance on a song prevents me from giving the app a five-star rating.