avicov the new aircraft (A350) are urgently required elsewhere so they will probably not be used DOH-LHR. There is an A380 scheduled for delivery at the end of the year and this will also probably be used on other routes.
The A333 was a 3 class aircraft and QR apparently wish to retain the F capacity as a back-up for the A380s. All other 3 class A330s have been refurbished and are now 2 class aircraft.