I have had an idea for a while and I think it would be a small, but great addition to the game. DeathTags!
With the new summon command and the not as new scoreboard commands, I think it would be easily possible to create these. What I am thinking they would do is make it so that if you kill a specific mob (summoned with a DeathTag), it would activate redstone. It would be a way to separate a mob from the others so that stat.kill would only apply for that one mob.

How this would work:

If a mob was summoned (Example): "/summon Zombie ~ ~ ~ {DeathTag:Red}", it would have this Death tag and when it was killed, a testfor command would activate redstone. First a scoreboard command like "/scoreboard objectives add KillZombieRed stat.killEntityZombie Red" then afterwards a testfor command like "/testfor @p[score_KillZombieRed_min=1].

The reason this would be a nice addition is that for example, someone is trying to add a boss mob that spawns minions via a clock and/or gives you the wither effect randomly during battle to their map and they want a way to stop the effects as soon as the mob is destroyed, but not if a minion is killed. This could also make some amazing death scenes! Like in Herobrine's Mansion, when a boss is killed, their speech and effects stay active. If DeathTags existed, they wouldn't be talking whilst they're dead and instead they would say their death speech and give you a key or something.

It's a very simple idea but could make some amazing things!