I think you are on to something. The problem with license tests is that you fail with no feedback until you get it right. When you don't already know how to drive, you improve by trial and error. If the game could tell you what you did wrong and how to fix it, it would really help you improve.
The game could identify problems in your driving technique such as braking too late or too soon, power at the wrong time, bad driving line, and so on. Then it could give you feedback on how to improve. Maybe combining the feedback with a replay of your run. For example, it could show you where you started braking for a corner and where the optimal point for braking was.
GT already includes indicators for the proper line, braking point for corners and so on. It just needs to identify how you have deviated from good driving technique and present that information to you.