I would like to know this as well - I tried looking elsewhere in the forums, and could not find anything. The patch notes suggest that it's always been a low threat heal, and the change was simply in the tooltip. Also, I found this old post by Vaneras (
WoW BlueTracker:) which suggests that the threat may be lowered by 50% (i.e. threat being only on your heal, not your target's, or viceversa).
I'm in a heated discussion with my raid leaders, trying to convince them that Salvation on Holy priests on Morogrimm is useless, as we can fade and Binding Heal when Murlocs spawn...