I say if someone was going to practice this kind of thing they should concentrate on getting the transition as smooth as possible before trying to make the shifts lightning quick. I know for me, my ability to shift quickly has come with years of driving and riding motorbikes.
Come to think of it I've been rev-matching for over a decade counting dirtbikes. But I'm sure it would still take a lot of practice to get it right on a track... which is where I would practice of course.