The 5 youngest QF B767's have dual GPS receivers integrated with Pegasus FMCs. Retrofit of GPS to the rest of the fleet would be fairly cheap but unfortunately the older FMCs are not capable of integrating with GPS and replacing them with Pegasus FMCs would be very expensive. A GPS receiver is embedded in the EGPWS and has a capability of supplying GPS data to other systems but the FMC limitation has prevented use of this capability.
Personally, I think that B777-300ER's would be a better option to make up for the lack of capacity until the B787 deliveries start.