So I was thinking....
Experience Shop
So when you reach lvl 100 in a skill you unlock a special shop for that skill. But instead of using graalts to buy the items you use your total exp to buy these items. Also once 100 (or what ever max lvl is) you don't stop gaining exp but instead the exp till next lvl=Infinite
The shop items could be like a gun a mele a pet several hats and other items.