Something like that might work if done carefully, but PLEASE GOD NO VATS!
Yeah it's not really VATS. it's just choice in finishers and one hit kills on weak opponents.
You'd still have to wear them down in real time... Just gives you a choice/variation in finishers.
EDIT:
Also at high level of skills (swords rank 100 for example) you'd unlock an ultra finisher unique to each weapon.
For example you'd beat the guy down with your claymore, then trigger the unique finisher, you would make him get down on his knees
then choose when you cut his head off with a click of the mouse. Maybe even let him live ? NO !!!