Pretty simple suggestion based on a few reasons:
A) It's not based on any specific caster stat.
B) Every blue-bar has it as a class skill (Well, and monks, that presumably would like the amp to finishers).
C) You've pretty thoroughly broken the dice in top-end content to the point where most of us are scrambling to take quicken anyway, making the skill obsolete.
D) You don't have to cook up an entire new set of items across all levels so folks can grow into the notion if they're starting from scratch or TRing.