This needs to be implemented as an option. You have so many people already fleeing TERA like a sinking ship to come to Guild Wars 2, this would be such a great thing to entice them even more so to come over.
En Masse had one thing they did great with TERA, and that was the combat.
The action style combat system they had was a refreshing change from tab targeting, and should be at minimum an option, if not the standard, of every MMO henceforth.