Rumors have now started regarding the Sony Xperia Z4 which is expected to be announced in early 2015.
Rumors claim that Sony will bring a 5.5 inch Quad-HD display to the smartphone. Sony is also rumored to use the Snapdragon 810 chipset. The device might be running Android 5.0 Lollipop at launch. Sony may also add improved speakers for good audio. A curved rear facing camera could also make it to the Xperia Z4. It is unknown if this device will be able to handle dust and water.
We must wait for the CES and MWC 2015 press events to see if any of these rumors regarding the Xperia Z4 are true.