I don't think this is a last minute buff (although it looks like that from player's point of view). We know they were testing lots of various SP buffs throughout, including the reverted MB buff. My guess is that they tested loads of buffs internally (MB, SW:P, maybe others we never saw) and just wanted to wait to see if SP would be good enough without it.
Then, when it became clear SP would still be low after the MB buff was reverted, they put this in instead.
My only rage is that this buff comes just as one of our healers becomes unavailable meaning I'll probably end up healing most of the time..