Instead of killing this golden egg (profitable premium trains) by imposing flexi-fares, IR should try to bring more and more paxs on these trains and earn much higher revenue/profit by
(1) Dropping flexifare altogether
(2) augmenting coaches in these trains
(3) rationalising the destination/composition/timing/stops of these trains,
(4)...
more...

increasing frequency as per requirement
(5) introducing new trains from non capital destinations as per requirement,
(6) Introduction of more SL LHB coaches which in general have high occupancy in premium trains his shall help run all the premium trains with max rake length which means more paxs carried and higher revenue for IR.
(7) If at all increase is required, then it is better to increase base fare to 120% of ME fares instead of current 115% for all seats/berths rather than by going into the proposed complicated arrangenment.