A driving coach that can be activated within menus or even replays, giving tips of what to do
Eg.
Brake earlier on corner 5
Too much break/not enough
Roll into ento roll out into second corner
Go wide
So this could be a very basic thing
Or Forza can get a bunch of professional drivers to do voice overs giving several points different lines to choose from according to which professional driver you choose as a coach
Different Coaches could also be micro transactional purchase, they would be extremely valuable.
This could also include coaches for tuning and performance parts