It was my chief criticism in beta, it's slightly amusing that a regen is instant cast yet less time efficient than a Cure III... you can basically only cast a regen on a tank when the tank is at full HP in a hard hitting fight.
There are other examples, and there are DPS examples as well.
The problem with this of course is that if you do let everyone have their instants off cooldown the classes (melee, acn/smn) that have lots of instant cast abilities receive a massive balance related boost, it's not really an option I'd like to contemplate when PvP is considered.
I'm all for reducing the GCD, but I'm not sure about making things instant cast not trigger one.