Once the roll out for the three mentioned above is completed, or at least near completion to their standards, then Sony will start another round of Android 4.4 updates for four more Xperia devices. Those holding onto a Xperia Z, Xperia ZL, Xperia Tablet Z and Xperia ZR will be happy to hear that in mid-Q2, that is May, Sony will start pushing Android 4.4 out for you.
An additional little bit of info also puts the Xperia T2 Ultra, Xperia E1 and Xperia M2 in the mix for an update to KitKat. They failed to offer a time line of any sort for those three devices.
Source: Sony Mobile