Definately a good idea for improving the offseason
I think this idea could possibly be expanded by offering full-team training sessions where you can figure if that star rookie will fill the void in your team.
Also, I think it would be good if they could expand on the rookie idea by not making random player progression, but actually if you work with players in the gym (do weights, run lines, practice free throws) there would be a chance of player improvement. The Player PKG that EA insists on using in the database could determine how likely the success of these training sessions would be.