Another idea related to this - create more swings in how a player progresses.
Here some illustrations of my idea. I'm going to make progression linear to keep this simple, and I'm not going to apply it to actual values really. The concept holds true even if you adjusted those pieces.
Baseline today - let's say potential moves a constant 20% of the way to it's final value each season.
0 20/60
R 32/64
2 44/68
3 56/72
4 68/76
5 80/80
Instead of moving a constant 20%, let's put a swing of +/- 25% on top of that. So the best case is moving 45% each season, worst case is -5% (assuming a boom player)
Best case scenario
0 20/60
R 32/69
2 44/78
3 56/87
4 68/96
5 80/100
Worst case scenario
0 20/60
R 32/59
2 44/58
3 56/57
4 57/57
5 57/57
Both of those would be pretty rare - you'd have to get the worst dice roll five times in a row. Let's imagine a few other interesting scenarios:
Late bloomer
0 20/60
R 32/59
2 44/58
3 56/67
4 68/76
5 80/85
Plateau
0 20/60
R 32/69
2 44/73
3 56/75
4 68/76
5 75/75
Roller Coaster
0 20/60
R 32/69
2 44/68
3 56/70
4 68/79
5 80/80
An even more interesting part of this is the doubt it could introduce sometimes whether a player is a boom or bust after the first training camp.
Boom Player, Worst Case Rookie Year:
0 20/60
R 32/59
Bust Player, Best Case Rookie Year:
0 20/60
R 24/61
You can't actually tell if you have a boom or bust in either of those scenarios.
Another outcome - it could temper busts. In the current system, a bust could look like:
0 20/60
R 24/56
2 28/52
3 32/48
4 36/44
5 40/40
In this system, a bust could be:
0 20/60
R 24/56
2 28/57
3 32/58
4 36/59
5 40/60
In summary, this could create a system where you introduce some doubt into the players final state after his first training camp, creates more interesting player progression paths, and gives potential for super-boom players.