I would suggest it is slightly unfair to suggest DIF has gone just because it isn't available on one particular service. I'm able to get this £615 WTP fare
This is down as TKN2T0M4 DUB to WAS, and down in Category 50:
BRITISH AIRWAYS SPECIAL WORLD TRAVELLER PLUS DUAL INVENTORY
FARES
APPLICATION
AREA
THESE FARES APPLY
FROM UNITED KINGDOM TO AREA 1.
CLASS OF SERVICE
THESE FARES APPLY FOR ECONOMY CLASS SERVICE.
TYPES OF TRANSPORTATION
FARES GOVERNED BY THIS RULE CAN BE USED TO CREATE
ROUND-TRIP/CIRCLE-TRIP/SINGLE OPEN-JAW JOURNEYS.
THIS RULE GOVERNS ROUND-TRIP FARES.
---
AVAILABILITY AND PRICE OF THIS FARE IS DETERMINED
BY THE LOWEST AVAILABLE ECONOMY BOOKING CLASS.
SEE GGAIRBAGDIF FOR FURTHER INFORMATION.
With DUB-LHR I can see some issues with getting fare bucket K on some services, but the above example is OK.