Empowered Smite
This is an idea for an empowered smite ability. This empowered smite ability would replace both of the summoner spells of anyone who: Got first blood; Got an ace (awarded to whole team); Got a pentakill.
Obtaining an empowered smite would give the owner the ability to smite an enemy champion, buff monster, or epic monster within 300 seconds of obtaining it. Against champions, this would deal 200 + 75% of their maximum health as true damage. Against buff monsters, it would instantly kill them. Against epic monsters, it would deal 50% of their maximum health as true damage.
This would be a one time use ability, so it wouldn't be too OP, although you could get it multiple times in one game. The idea behind this is to encourage team play by rewarding it for aces as well as first blood, also encouraging early game strategic planning.