Sony hasn't made any major changes to the Xperia Z series over the last few years, there has been numerous improvements spec-wise, but there hasn't been any real game changer added to the Xperia Z family. This may soon change with Sony reportedly aiming for a more "premium" feel, by changing the chassis material from glass to metal, which will feel sturdier and will be less prone to breaking while also making the device lighter as well. Not to mention, following the recent trend set by other companies like Samsung, with the Galaxy A5. A fingerprint sensor is now also being rumored to be featured in the upcoming Xperia Z4, Sony opted to add the sensor in the power button, an unusual position when compared to other OEM's flagship devices which normally embed it onto the home button.
Fingerprint scanners was a huge trend in 2014, many OEMs like HTC have been adding fingerprint scanners to several their flagship devices like the recently announced HTC M9+. It seems now, that Sony will try to follow that same path, but changing things a bit with the goal of making the device more functional. The new Xperia Z4 will feature the fingerprint scanner in the power button, that is something the market has only seen once in a mobile device (the Saygus V-Squared). There are some doubts on the placement of the sensor, mainly because Xperia devices have really minimal buttons, making the surface area of the fingerprint sensor really small which can lead to the misinterpretation of the user's fingerprint. If Sony manages to implement a sensor that can provide accurate readings most of the time, the new fingerprint sensor will surely be a hit with users of the upcoming Xperia Z4.
Sony will also change the chassis material to aluminum, coming from glass, a trend that has been greatly adopted by the industry. The company will not only add a metal frame to the phone, it will change the material of the whole phone's body akin to the Samsung Galaxy A5. Users are expected to be able to see the new Sony Xperia Z4 for themselves around September.