Skill Cap Breakers
Skill caps should be breakable with statistical achievements, not only via coach abilities. This would be an offseason enhancement at the same time as the Development Trait changes. It would naturally only apply to the top 5-ish players on the team because those players find themselves around the ball most of the time. Wear and Tear would naturally govern this mechanic, but limiting reps.
As an example, if a QB has an accuracy skill cap, but throws 100/50/25 short/med/long completions in a season (arbitrary numbers), it should break their Accuracy skill cap by one. To continue the QB example, throw power cap breaks could be number of passes thrown at 90-100% of full power, or completed passes.
It could scale with star level of the player: low star players should have higher stat requirements for each cap break. It should probably be difficult to work on breaking more than one skill group. Either choose Throw Power or Throw Accuracy, breaking one progressively increases the difficulty of the next within that tree, as well as other skills.
More random examples: Speed increases from TD runs longer than 25 yards (obviously they weren't caught), Catch from successful catches, tackle from total tackles in a season (EA already has a tackle grade working behind the scenes, could that factor in?), etc. The point here is a playing scheme that prioritizes a certain style should allow players to progress further in the skills trained by that style.
I would NOT tie cap breakers to player awards (POTW, Heisman, etc).
This mechanic could provide a new and rewarding challenge for users who play ever game. Brings an element of RTG to Dynasty.