I have seen various iterations of this idea that never seem to gain traction, but I can tell you that as a new user to Yousician it would make or break my subscription.

When starting a song which you MUST score high enough on to proceed, I struggle to press start with my mouse, get my pick out of my mouth, and get my hands in position on the guitar before the 8 beats or so before the song begins. There could easily be a setting that could be added which would adjust the number of beats that are played before the notes start. You already have the pre-song beats in place, so just add a setting to adjust how many.