Big fan of the "Road to the Show" game mode, I love being able to create my own character from the huge possibilities of choices.
I would love to see a mechanic brought into the game that has your created character grow facial and head hair over the season (Kind of like the hair growing mechanic in Red Dead Redemption 2) or even grow in length of the course of the season with the option of cutting it or letting it run wild.
Some MLB players are superstitious when it comes to their hair and I think this mechanic could add another level of immersion to an already amazing game.