Never spoke about Holy and Tank healing there
First information we had (written on wowhead comments as well) is that HOT is not stacking. In this case only holy would have taken any advantage of the bonus since they are using FH as well on multiple targets for raid healing (CoH, PoH, PoM, Renew and FH are big part of the cycle right?). In this case : multi-free-HOT = win for holy.
Playing disc and tank healer, I avoid as much as I can to lose grace stacks on the tank so helping for raid healing is mostly PoM/ PW:S and renew sometimes (of course if FH is required I use don't get me wrong ). So no stack would mean only permanent hot, let's say something betwenn 150-250 HPS which is not so bad but not terrific regarding bad fitting of T10 pieces with disc (SPI ugh :).
With stacks now it is really worth taking it^^