The shadow priest rotation is already messy in p3. It take ages before we can start our actual rotation with alle the utility stuff we got to pop, and now in p4 the rotation will be even messier where you want us to use both Mind flay and Mind spike with the tier 1 6p set bonus, and also VT quite often cause it only has a 15 sec dot timer.
A suggestion would be to somehow combine Mind Flay and Mind blast into one spell. Nobody wants to be using both. As it is now on the PTR it will be a horrible rotation.