Seems complicated to me and often not adequate. There are builds which offer several reactions for one char. You often have to consider what reaction is best in a given situation. Do I choose a lvl 3 or a lvl 4 counterspell, or do I use tadpole retaliation? Or maybe something else I even don't know. A turn based game should offer time to think. I would be more or less annoyed by a slow motion alternative.
On the other hand, if such an alternative could be a toggable option for people who like it, why not? It's then a matter of how many would like it and how difficult implementation would be.
