What he said ^^^
Would love if there was some sort of coaching staff recommendations telling what the status of each player is. In terms of what they have progressed most at or what they need to work on most. And then incorporate that with some sort of special spring training workout routines. NBA 2k does this with an offseason training camp interface. Maybe you get 3-5 per season, that you can send a player to to improve their ratings in the related categories.
So you can send that light hitting prospect to a weight training "camp", and get a few points added to his power ratings. Or that Power Hitting first baseman that strikes out a lot can go to a pitch recognition "camp" and get a few points added to his contact and discipline. Or the super-speedy center fielder with the unreliable glove can go to a fielding camp and get a few points added to their fielding and reaction ratings. Etc.
It would be nice to have some sort of off season or spring training workout programs to develop players between seasons. I know others have suggested adding Arizona Fall League or Dominican League. Same concept, having some sort of facility to train up players between seasons.