Suggestion is to give additional training level, lets call it intensive training, it gives 2x bonus on training stats in case if selected. Also, if player is selected for intensive training, he will not be able to play any games in that day.

Reason: if you check best player currently, he has AVQ=86 with much additional skills which can be learned, so there are space to increase training speed. Also, it will give option to train faster young players to be good substitutes. For people who is worried about salaries will give option not to use this training

Salaries are not the problem, as they fund the prizes. The income would grow accordingly.

The problem is the variability in the players' skills... what happens if the top teams can bring all the relevant skills of the players close to 100? They would all be almost equal, and tactic settings wouldn't matter anymore, as the players have no weak points. It would turn the game into a lottery.

There is not much room for further growth in my opinion

dont think it will be so much increase in skills, currently players who play game getting 1.5 coefficient, in my proposal players who dont play and go to intensive training wil get coefficient 2, dont think that even 5* players that all time train can reach AVQ 95. 

Bad idea!
For now you get better younger players that can compete against the older players but what would you do over about 10 seasons? Keep increasing training boost?

I prefer keep this training system.