A new firmware update recently started to roll for the Xperia Z2 (D6503) in the form of build number 17.1.2.A.0.314. Whilst the Android build remains at version 4.4.2 KitKat, Sony did work through a number of changes including improved voice call quality, touch performance and charging when the battery is low.
One of the issues for some, was that none of the recent root methods worked on this latest firmware. However, thanks to Japanese developer ?@cubeundcube this is no longer an issue. An update to his rootkitXperia tool kit manages to root the Xperia Z2 without any issues, even for those with locked bootloaders.