You would have to be skilled in magic to use this ability.
I think that would be a little unfair to warrior & stealth/archer type classes.
Like i said just maybe not do exactly like vats,where it pauses the game....do it so the game knows that your next hit/strike etc,would finish your enemy off.
Just give us the option to use finishing moves & watch them in slow mo from a different angle,but not everytime you kill someone...make a little rarer,so its not as repetitive
just capture the cinamatic feel of a kill ( similar to fallout ),but dont let us pause the game.
Maybe how often that happens could be down to a certain stat ,higher luck,or the enemies fatigue etc.
It would add a liitle to an already great game if done right & not every kill.
Just my view
It would also be a great way for people to share funny moments or show some great kills etc.