People want dual spec so they can do a dungeon, and then swap and raid. You’d added a CD that removes that functionality.
Or maybe you only really need an extra healer for one fight that’s been tough for you? Well a CD removes that ability
What if you want to do arena before raid? no
Changed specs for a pug you signed up for, and the tank leaves and needs a new one…well so much for dual spec it’s on CD
It’s a garbage idea that destroys the whole GD point of dual spec