So, thieves have 4 traps and only one of them is really much good in tournaments (Shadow Trap).
I’d propose a change that looks like this:
Traps have two stages: the first is where you place it on the ground.
After it’s placed on the ground, if an enemy is standing in the trap, you have a second option to activate the trap and it activates on the enemy/enemies inside of the trap.
This would add an element of active play to traps, making them both harder, yet more effective to use. Plus, laying down a tripwire and cutting a zerg in half would be pretty funny.