My personal opinion is that you should be rewarded a medal called “Spinal Tap” if you get a one shot kill with either the Shotgun or the Scattershot, the only thing is that it has to be in the enemy’s backside, very similar area to an assassination. What does the Halo Community think?
I personally think that would be a pointless medal. However, it would actually fit Halo 4 pretty well.
Edit: By the way, I don’t believe it’s even possible to add new medals in.