As economists can't agree on this (like everything else in economics) it always leaves the door open to an oscillation in policy decisions between different approaches. Equally hard to see that these are vital.
I am not sure if GDP can be accurately measured in this manner. I mean productivity is one of indicators closely watched by market, but it is related to GDP and calculated using GDP figure. This is why I cannot well understand how they are exactly going to use productivity as measure of GDP?