While I'm always up for assassinations (big Assassins Creed fan here) something like you described would probably make the T rating questionable. Unless it wasn't bloody? but even then something that puts such emphasis on the brutal knife stabbing would look kinda silly without blood.
I remember talking with someone else about an idea like this before; can't remember if it was in a topic here :\. Anyway, it was something about melee kill animations or something like that. Wish I could remember because it was an idea I liked, but I can't remember at all why I liked it. If I remember I'll post again later assuming it does have something to do with the topic >_>.
Scientists investigate that which already is; Engineers create that which has never been -Albert Einstein Wanting: Golden Sun DD, Conduit 2, Starcraft 2, Civ V
Uh mabey not quite like that but it would be cool cause its one punch in the back for a kill have a little mabey special assassination like cover their face with the hive cannon and blast a few rounds in them