I've proposed this idea in the past to Luke warm receptions. If trophy size fish are the goal, the only proven method is slot limits. Any body of water has a finite carrying capacity. For example, if a certain body of water can sustain 1000 pounds of fish per acre, it could be 1000 one pound fish, 500 two pound fish, 333 three pound fish or any combination.
Size limits are a double edge sword. On one hand, some fish grow to trophy size while most fish are taken out when they reach the length limit.
On the other hand, size limits load the lake with large amounts of under size fish.
If the goal is growing trophy size crappie, a slot limit would work best. Take a bunch of the smaller fish out so they are not competing for the carrying capacity of that body of water.
Put a slot on the most productive breeding size. They go back in. When fish reach trophy size, they are near the end of their life cycle and can be taken without harming the balance.
This method has worked for green carp lakes for years. I know some will not like it because you will have to put back nice fish.
If trophy fish are the goal, this is the way to make it happen.