I just lost an hour writed message to some deconnexion so I'll just sum up what I think could benefit to this game.
Somehow increase the pace of the game.
New generation players don't want to wait 1 or 2 IRL years to get the impression they can compete. You may decrease the number of game in a season (only one match against each team by conference is an example of what you could do). That would include a proportional increase of training speed (which would also fit the younger players by giving them more rewards every week) and maybe the creation of a 2nd national cup for the lower ranked team.
Add real rotation management and change the coach system.
I like the "difficulty" of fully training players but that take part of the fun which is a bad thing regarding new players.
Adding real rotations to the game would only render it more realistic and allow players to train in 2 games instead of 1 (playing 38 and 10 minutes in 2 games instead of 48 minutes in one).
Also, you could permiss players to receive training at every position. It's a pain to play a player for a full year (minimum) at an unfitting position and that only take the fun away.
But I'm also for that old system that wants you to make a choice between training and competing.
That's why you could change the trainer system. You could go for the "compete coach" that would allow you to train 2 mono/4 duo players at every position.
Or you could go for the "training coach" that would allow to train up to 3/6 players but with fixed position. And let's say players that way would only need 45+ minutes at a position to receive full training (that way you would more effectively train 3/6 players and not 2.5/5).
Add a "hidden potential" to the players.
Actually, let's say you can max a Hall of Player type player by the age of 28 (just an example, I don't know if that is the case).
With the "hidden potential" (low, medium, high), you could max the same player at 25, 28 or 31 years old.
How that ? Not by increasing their training speed, but by decreasing their decrease in training speed (consequently after the age of 21).
But the hidden potential would only be known after 2 full season of training in the same team.
And of course :
Give people the mobile app they ask for.
That would bring new players from the app store and increase their bonds to the game with the constant notifications.