Its a blunt instrument that has be tried before and will end in tears.
There are lots of things companies can do to reduce fuel comsumption other than just asking pilots to take less. Controlling the weight of items on the aircraft (rubbish, catering loads etc), regular engine washes, aircraft husbandry to reduce drag. All of them cost money and effort but they do work.
Ranking pilots on their fuel loads does not take into account the risk management on the day. It is quite possible for pilots to take high risk fuel loads and be lucky and under this type of system they will be rewarded for what are in fact really bad choices. Probability being what it is though when you cut corners on a large number of flights the company will inevitably have incidents and if this results in an accident the company may not survive. Penny wise, pound foolish.