Bannock,
Maybe part of the reason why MPA/MMA is such a sacred cow for 2015 is the political aspect, which includes avoiding providing the opposition with ready ammunition.
The MRA4 will have been scrapped by the 2010-2015 government, which provided the arguments as to why this could happen. It will be a different government, the 2015-2020 one, that restores (maybe?) the capability. Thus potentially avoiding accusations of a U-turn?
Just a thought.