Seems to be this should simply be built-in as why you'd opt for slower health response is beyond me.
There is a very serious performance penalty to the QuickHealth mechanism for a very little speed improvement of health bar update. This is the main issue I have. But there are other valid reason not to implement this.
For instance, I am quite certain that using QuickHealth only improves the heal throughput of the one using it. There is no improvement to the ability of the raid to win a encounter.
The whole idea from QuickHealth is that healing is supposed to be simply reaction, but it's not. I think that depending too much upon quick reaction to health bar is the wrong way to heal.
Finally, Cataclysm increased health pool and encounter philosophy will make QuickHealth even more irrelevant than it is now. Spending a lot of coding time on it now would be a waste of time.
Anybody willing to can implement a QuickHealth addon to Grid2. That would be somewhat easier to do than for Grid, I'm confident of that.